Soil means different things to different people. Earth scientists see soil as mineral or organic material that is formed on Earth's surface by dynamic, complex processes. Engineers think of soil as material to build on and are concerned with moisture conditions and the ability of soil to become compacted and hold weight. Agriculturalists think of soil as the top 15-30 cm of Earth's surface to grow crops, while others think of soil as dirt which one plays in or gets "dirty" from.

Soil scientists, or pedologists, are primarily interested in the way the five soil forming factors (parent material, climate, topotgraphy, organisms, and time) affect the properties of the soil in its natural, undisturbed state. However, Forensic Geologists study soil that has been disturbed or moved during human activity, to solve crimes. Forensic Geologists obtain soil samples from crime scenes and other sites in question where soil may have been transported, by vehicle or by foot perhaps, and are suspect. Soil characteristics are diverse and this diversity enables Forensic Geologists to use soils as evidence in criminal investigations.

THE FIVE SOIL FORMING FACTORS

Soil formation and the properties of the soil are the result of five key factors:

1. parent material: The material from which the soil is formed. Soil parent material could be bedrock, organic material, an old soil surface, or a deposit from water, wind, glaciers, volcanoes, or material moving down a slope.

2. climate: Heat, rain, ice, snow, wind, sunshine and other environmental forces break down the parent material and affect how fast or slow soil processes go.

3. organisms: All plants and animals living in or on the soil (including micro-organisms and humans!). The amount of water and nutrients ,plants need affects the way soil forms. Animals living in the soil affect decomposition of waste materials and how soil materials will be moved around in the soil profile. The dead remains of plants and animals become organic matter which enriches the soil. The way humans use soils affect soil formation.

4. topography: The location of a soil on a landscape can affect how the climatic processes impact it. Soils at the bottom of a hill will get more water than soils on the slopes, and soils on the slopes that directly face the sun will be drier than soils on slopes that do not.

5. time: All of the above factors assert themselves over time, often hundreds or thousands of years.

The way the five soil-forming factors interact is always different from one place to another, so soils differ greatly from each other. Each section of soil on a landscape has its own unique characteristics. The face of a soil, or the way it looks if you cut a section of it out of the ground, is called a soil profile, like the profile of a person's face. Every soil profile is made up of layers called soil horizons. Soil horizons can be as thin as a few millimeters or thicker than a meter.

Soil profiles and their horizons change as you move across a landscape, and also change as you move downward deeper into the soil at one location. In fact, soil samples taken at the surface may have entirely different characteristics and appearances from soil dug deeper in the soil profile. One common reason soil horizons are different as you dig deeper is because of mixing of organic material in the upper horizons and weathering and leaching in the lower horizons. Erosion, deposition, and other forms of disturbance might also affect the way a soil profile looks at a particular location.

Now, you may be wondering how many soil types are in existence. The United States Department of Agriculture (USDA) maps and collects soil data at many different scales. According to the USDA, there are over 50,000 different varieties of soil in the United States alone! Since parent material, climate, organisms, and the amount of time it takes for these to all interact varies worldwide, soil combinations also vary worldwide. Forensic Geologists have their work cut out for them. So, how do Forensic Geologists use soil to solve crimes? Read on!

TECHNIQUES USED BY FORENSIC GEOLOGISTS

Soil samples must be carefully collected, handled at the crime scene and then compared by a Soil Scientist to ensure that the soil samples can be useful during an investigation. To compare means to understand that no two objects on Earth are exactly the same; however, two soil samples (or other Earth material) could have originally come from the same place, but a portion of the soil (or other Earth material) could have been removed to another location during human activity. Forensic Geologists look for uncommon and unusual particles, or unusual combinations of particles, in soil samples and compare them with similar soil in a known location. Depending on the type of soil and the minerals present, in addition to grain size, the Forensic Geologist employs intensive observational methods and analyzes crime information to deduce whether a soil sample can be used as evidence.

Often, the forensic geologist must determine the distribution of particle sizes in samples for use during comparison studies, mineral studies, and color studies. To perform these studies, the forensic geologist uses methods that GLOBE students and teachers use to study soil soils. Soil samples are taken from intact soil profiles whenever possible and then characterized for structure and texture. The Forensic Geologist uses sieves, graduated cylinders, and hydrometers to perform soil particle size distribution analyses and also performs bulk density tests to determine soil porosity. If the samples collected are discovered to have cementing agents such as calcium carbonate (CaCO₃), iron (Fe), or organics which hold the soil particles together, then these cementing agents are removed using special chemicals.

INSTRUMENTS USED TO STUDY EARTH MATERIALS

Approximately fifty common minerals as well as some less common minerals can be seen by the naked eye, but using a lens or low power binocular microscope enables the Forensic Geologist to better detect mineral properties and provide more accurate mineral identification. A common instrument used to study thin sections of rock, mineral, and soil samples is a petrographic microscope. Thin sections of Earth material are mounted on a glass slide and viewed with the petrographic microscope as light filters through its special attachments.

Scanning electron microscopes (SEM) and electron microscopes also can be used to examine particles over 100,000 times their original size making them very useful. Forensic Geologists and lab scientists are able to see, in greater detail, the characteristics and variations of soil samples. Fossils and pollen spores that collect in rocks and soil can also be seen, and are sometimes useful indicators when studying soil samples. In fact, scientists were not able to see the distinct differences in very small fossils nor scratches on mineral grains until the SEM was invented. The electron microscope and scanning electron microscope are very useful to the Forensic Geologist who must analyze soil samples with great precision and make important decisions that affect peoples lives.

CRIMINAL CASES SOLVED USING EARTH MATERIALS

The Federal Bureau of Investigations (FBI) has collected and studied soil samples, minerals, and other Earth material for criminal investigations since 1935 and thousands of cases involving Earth materials are studied in the United States each year. Throughout the world soil is usually collected at crime scenes, is routinely studied at crime labs, and is often used as physical evidence during crime trials.

Following are some real-life stories of crimes that were solved using Earth materials, thorough investigative work, and dedicated, professional scientists who studied soils and geology to become knowledgeable in their field. So you see, there really is more to soil than what's under foot!

A crime had been committed in the foothills of the Rocky Mountains, near Denver, Colorado. One month later a burning vehicle was found at a dump in New Jersey (on the East Coast of the United States). Soil samples were taken from the fender of the burning car and were studied by Forensic Geologists. Analyses of the soil samples showed there were four layers of soil that had built up under the burning car's fender. The outer, most recently deposited layer of soil was from the New Jersey dumpsite. The three inner layers of soil contained minerals from the Rocky Mountain Front area near Denver, Colorado (If you don't know geography, now is a good time to pull out the United States map and take a look).

Forensic geologists obtained 360 soil samples from the Rocky Mountain Front area to compare them with those found under the fender of the burning car in New Jersey. Soil samples were also taken from the victims ranch. One of the three inner layers of soil under the suspect's car's fender matched the soil sample Forensic Geologists obtained at the crime scene. The second inner layer of soil under the suspect's car fender matched the soil sample Forensic Geologists obtained at the victim's ranch. The first inner layer of soil did not match any of the 360 soil samples taken by the Forensic Geologists but was determined to have originated from the Denver area. The suspect was convicted and jailed based upon the results using soil sample comparisons.

In the case of stolen potatoes on the east coast of the United States, a suspect who possessed the questionable potatoes was convicted of stealing them once analysis of the soil on the potatoes determined that the superphosphate in the soil that was clinging to the potatoes matched the soil from the farm where the potatoes were grown. The farm's soil contained a significant build up of phosphate because the farm was heavily fertilized with nitrogen, potash, and phosphate (phosphate doesn't leach out of the soil as readily as potash and nitrogen).

In another case, tobacco was reported stolen from a farm. Soil samples were taken from the farm where the tobacco had been stolen, and samples were also taken from the leaves of the stolen tobacco and from the suspect's farm. Soil comparison studies indicated that the soil on the stolen tobacco leaves did not match the soil samples taken from the suspect's farm, but matched soil samples taken from the farm where the tobacco was reported stolen. The suspect was arrested based upon the resulting soil sample comparisons.

Microscopic fossils called diatoms were once very prominent on Earth, and collectively deposited to form a sedimentary rock called diatomaceous earth. Some manufaturers use diatomaceous earth for insulating safes, that are used to store valuables. Burglary crimes have been solved by examining white specks from suspects' hair and clothing to determine that the specks were actually diatoms that came from broken safes at crime scenes, and not dandruff as the suspects had claimed.

If you would like to learn more about the interesting and exciting world of soil, check with your local library or on the World Wide Web. You just might learn something you'd never thought about before!

Information contained in"Secrets Hidden in Soil" was derived from "Forensic Geology" by R. Murray and J. Tedrow, Rutgers University Press, 1975. ISBN 0-8135-0794-4. Also, special thanks to Dr. Richard Arnold, USDA, Natural Resource Conservation Service/Soil Survey Division, Washington, D.C.

Source: www.gsfc.nasa.gov

Analytical Techniques for the Comparison of Soil Samples:

The forensic technique commonly used for the analysis of soil samples is the density gradient tube technique. Glass tubes measuring 6 to 10 millimetres in diameter and 25 to 40 centimetres in length are filled with several layers of two liquids mixed in varying proportions such that each layer has a different density. An example is the mixture of tetrabromoethane, which has a density of 2.96 gmL-1 with ethane, with a density of 0.789 gmL-1. Using varying proportions of each, from pure tetrabromoethane (bottom of the tube) to pure ethanol (top of the tube) provides a density gradient into which the soil specimen is added. The soil components then sink to the layers corresponding to their own density values and the distribution of particles can be compared between soil specimens. Carry out the analysis...

nductively coupled plasma coupled to mass spectrometry (ICP-MS) analyses the elemental composition of the soil. The plasma is formed by argon gas flowing through a radiofrequency field where it is kept in a state of partial ionisation, i.e. the gas consists partly of electrically charged particles. This allows it to reach very high temperatures of up to approx. 10,000ºC. The sample being analysed is introduced into the plasma as a fine droplet aerosol. ICP-MS is the combination of an ICP with a mass spectrometer (MS). The ions generated by the ICP are directed into the MS, which separates the ions according to their mass-to-charge ratio. Thus, ions of a selected mass-to-charge ratio can be detected and quantitated.

The coupling of ICP-MS shows many advantages over other analysis techniques. Benefits of the ICP over other radiation sources include improvement in excitation and ionisation efficiencies and the reduction or elimination of many of the chemical interferences found in flames or furnaces. Mass spectrometry generates a large amount of information, has high throughput capabilities, high sensitivity and low limits of detection. ICP-MS is capable of multi-elemental detection which reduces analysis time and therefore increases sample throughput. ICP-MS is one of the few analytical techniques that permits that quantitation of elemental isotopic concentrations and ratios. It can achieve very low limits of detection (e.g. 1-10 ng L-1)

The geographical location of soil samples gives rise to variation in their elemental composition. Thus, soil samples can be compared to samples collected from their suspected sources of origin. Carry out the analysis...

Source: www.hull.ac.uk

Analysis and Collection of Soil Samples:

Written by Katherine Steck-Flynn

Back in the nineteenth century Edmund Locard developed the theory known as the "Locard's Exchange Principle." The theory in short states that when ever someone comes in contact with another object or person there is a minute exchange of particles that, in theory, can be traced back to a victim or suspect (Block 1999). In a crime context, that evidence can confirm or disprove a hypothesis of involvement between a suspect and a victim.

Locard described these particles as dust or dirt but today it is understood to include all soil borne trace evidence. Trace evidence can include blood, hair, fibre, dirt, glass particles and any other minute particles at a crime scene.

It would be nice to think that this forward thinker, Locard, moved beyond his Principle to developed the idea of soil analysis but he didn't. His mentor and friend Hans Gross published articles almost simultaneously with Sir Arthur Conan Doyle, the author of the Sherlock Holmes Fictions, regarding soil analysis (Block, 1999)( Nickel & Fischer, 1999) To Edmund Locard's great disappointment both Arthur Conan Doyle and Hans Gross beat him to the punch on the evaluation of soil as a forensic tool. However, Locard's zeal for the use of trace evidence in forensic investigations led to a life long study of the classification and identification of soil samples (Block, 1999).

Since its dawn in the late 1800's the analysis of soil has grown into a multidisciplinary field of forensic study. Modern analysis of soil may involve geologists, entomologists, toxicologists, biologists, botanists and a myriad of other experts.

Soil may be understood as just that: soil. As such it has a value in forensic studies. However, soil may also be understood as a repository for non soil contaminants which can yield valuable information about crimes. In forensic analysis materials can be grouped in several ways and each lab has its own way of subdividing these groups (Chayko & Gulliver 1999). In general soil borne materials can be considered organic or inorganic. Both types are found in soil. Further refining of these classifications where soil is concerned is to break the groups into mineral, biological or synthetic matter.

Soil is considered trace evidence. Soil is made up of disintegrated surface material which can be organic, mineral or synthetic. The ratio of the mineral content compared to other matter in the soil can be very site specific. The ratios of mineral, organic and synthetic matter can vary even with in a few feet (Chayko & Gulliver, 1999). Sandy soils look, feel and behave quite differently from clay soils or peaty soils. By profiling an array of characteristics of each soil, it is somtimes possible to attribute those characteristics to a specific location (Steck, 2004). Soil samples when properly taken can tell an investigator a lot about where a victim or suspect has been. Analysis of soil samples taken from vehicles can also tell an investigator about where a vehicle has been. Analysis of foot wear, clothing and tires can also place a suspect or victim in a particular location.

Collection of Samples

Collection of soil samples will depend on the circumstances of the crime. Indoor scenes will differ markedly from outdoor scenes in the type of evidence that can be recovered and the way in which these samples are collected.

At indoor scenes there may be footprints in soil or in dust. Samples made by footwear should be photographed to scale before being recovered. The particle samples can best be collected using a vacuum method. The samples can be vacuumed with a portable vacuum cleaner equipped with a special attachment. The attachment has a metal screen on which a filter paper is attached. The area is vacuumed and the filter is removed and labeled with the date, location, time and name of the technician who operated the vacuum. The vacuum must be thoroughly cleaned between samples. Cleaning can be fairly easily done with handhelds where the parts are easy to access. Reference samples from the surrounding area perhaps including flower gardens, points of entry and exit and alibi locations should also be taken.

Information on obtaining these specialized vacuum attachments can be obtained through Sirchie Laboratories Inc. in Youngsville N.C..

In the case of a break and enter or other crime at a home or business it is useful to know how the perpetrator entered the building. For example, if the perpetrator stood in a flower garden outside a window this indicates a stranger. If the perpetrator walked up the front lawn or to the back door this could indicate someone familiar with the property. Possibly the perpetrator knew no one was there being familiar with the owners habits. The soil on the shoes of a suspect (or left on a carpet or floor) can indicate the direction of travel and the mode of entry. This type of evidence is most useful when a suspect can be immediately identified before the soil is lost from the footwear.

Soil evidence from a victim or suspects clothing can indicate an association between victim and suspect. For instance, if a suspect lives in a particular neighborhood with a specific soil profile and this profile matches one found at a crime scene or on a victim, then one must suspect that the suspect left that sample at the scene.

"Double transfer" is even more convincing. If soil profiling to a suspects home territory is found on a victim or in their home and soil from the victims home territory is found on the suspects clothing or footwear the probability of the suspect having been at the crime scene increases dramatically. The mathematic probability of two matching profiles being found at both scenes by coincidence increases. For example the probability of transfer to one site occurring by coincidence might be 1 chance in 800. When double transfer has occurred the probability of that occurring by coincidence becomes 1 chance in 64,000 (Crocker, 1999).

Inorganic or manufactured matter found in the soil recovered from a suspect's footwear or clothing can be very site specific. Particles of glass, rubber and other industrial products can be used to link a suspect with a particular location. In the not-uncommon case of crimes at industrial locations this can be particularly useful.

How to collect Samples

As already mention in the indoor scene vacuuming can be used to collect samples. The methods of collection will vary from scene to scene. In a break and enter where house plants are found upset a sample of the soil may be used to link the suspect to a scene. Soil from the garden or yard can also be used to track the suspect's direction of travel and point of entry. Most garden soils are unique. The gardener in charge will have added some favorite materials (sometimes specific to particular plants) in order to improve the garden. The materials tend to be different in every garden. Some gardeners might use compost while others might prefer ammonium pellets, sand, peat or wood chips.

Samples taken from the interior of a vehicle can indicate many things. A soil sample from the gas or brake pedal of a vehicle can link a suspect to a location. Soil from a trunk or backseat can indicate digging. When graves are dug to hide bodies the various levels of the soil are disturbed. If the suspect lays a shovel on the back seat or in the trunk the soil from the lower levels of the grave may be deposited on the seat or in the truck. Soil from tools such as shovels should be preserved in the state it was found. The entire tool should be packaged in protective material then enclosed in plastic. Finally the entire tool should be placed in a wooden or cardboard box and transported to the lab.

Sampling methods may need to be adapted when the scene is outdoors. If the challenge is the recovery of remains, soil samples should be taken at regular intervals up to 100 yards from the gravesite or point of recovery (Saferstein, 2004). Usually a grid search is set up and samples can be taken from each square of the grid and labeled as to which grid it was taken from.

About a tablespoon of soil should be enough for most modern tests. Usually only the surface soil needs to be sampled. The exception to this is in the case of a buried body, In this case soil samples should be taken at regular intervals as the remains are exposed. After the remains are removed from the gravesite the bottom of the grave should also be sampled. It is important to note that a new shovel, spoon or other scoop must be used for each grid and sample. Should the same implement is used serially, uncleaned to recover sample then Locard's Principle is at work again and cross contamination will render your samples useless.

Samples should be placed in plastic vials for transport. If it is not possible to transport the samples immediately they should be allowed to air dry before transport.

A special note for gravesites is that if insect evidence is present the vials should be labeled in pencil rather than pen. The specimens will likely be preserved in alcohol which if it leaks onto the label will destroy ink from pens. Without the label as to the time and place of collection your sample is forensically worthless.

Outdoor scenes often involve vehicles. There are several ways of collecting soil samples from vehicles. Vehicles involved in accidents will sometimes leave lumps of soil from under the wheel wells and fenders on the road way. These lumps should be collected intact and wrapped in protective material to minimize bumping during transport. The purpose behind this is to preserve the layers that have built up to create this lump of soil. A soil analyst can read these layers and know where this vehicle has been. The analyst may also be able to match the layers in a lump of soil to a particular vehicle. I can't help but think this would have been very useful in tracking Ted Bundy or Henry Lee Lucas in their cross county travels.

Clothing and footwear should be collected intact. No attempt should be made to remove soil from clothing, footwear or tires. If these items can be removed intact they should be placed in a paper bag or enclosed in a druggist's fold and then placed in a paper bag. Care must be taken so that the paper bag is protected so that evidence is not lost through holes in the bag. Some evidence can be placed in plastic bags but is must be completely dry. Wet samples placed in plastic with quickly degrade and rot and become useless. Plastic does not "breath" to allow passage of moisture and air. Paper on the other hand will allow moisture to escape preventing rot.

Lumps of soil stained with blood, semen or other biological samples should be collected intact and transported to the lab as dry samples. Any samples containing suspected biological material such as blood, flesh, semen or hair must be clearly labeled so that the analyst at the lab can take precautions to preserve this material. Biological specimens in soil must never be heat dried.

The only time a sample should not be allowed to dry is when insect evidence such as maggots are present. In the case of maggots there is a very specific way of handling this evidence. Samples containing maggots can be placed in aluminum foil with a small piece beef liver and placed in a plastic container. There must be air available in the container. These samples must be sent to the lab immediately. The specimens can be placed in a thermally protected case such as a cooler. Attempts should be made to protect the samples from extremes of heat and cold. Never use dry ice with biological or entomological (insect) evidence.

In the Laboratory:

In the lab items from the victim and suspect should be examined separately. Ideally the items and samples from the victim and suspect should be processed in different rooms. The personnel handling these sample should be assigned to one or the other. If this is not possible then the person handling the material should take extreme care to avoid cross contamination of the samples.

The laboratory staff will evaluate the soil samples in several ways. First the mineral content will be tested. Some experienced analysts can moisten a sample and feel the soil. Based on feel alone they can tell the ratio of mineral and organic content. Microscopic examination of soil samples will subsequently reveal the type and nature of the mineral, biological and synthetic content of a sample.

Such talented analysts are not always available. Then, there are several standard testes which can identify the type and origin of the sample. The first and probably the most common is the density gradient tube. Two different liquids are added to a glass tube in various ratios. Each ratio represents a different density. The soil sample is poured into the tube. When the various particles reach a level in the liquid where their density is equal to the liquid the particles become suspended. This creates a unique profile of bands in the tube which can be matched to other samples.

The samples may also be tested using heat to test the point at which the sample will undergo an exothermic reaction or an endothermic reaction. The sample is heated in a special furnace to various temperatures. In an exothermic reaction the sample essentially burns and releases heat. In an endothermic reaction the sample will absorb the heat. Each sample from different locations will have these reactions at different temperatures according to the mineral, biological and synthetic content.

Electron microscopes can be used to reveal the crystalline structures of minerals and synthetic material in a sample of soil.

Nuclear Resonencing and Mass Spectometry are also methods which may be used in the Laboratory.

It is important that the crime investigators and the laboratory analyst communicate properly. Perhaps this happens best when the laboratory head is knowledgeable about investigations and is the contact person for investigators. The head can be briefed on the questions and issues of the case and then direct the laboratory personnel as to the direction of the inquiry. The investigators may want to know if sample #12 and sample #76 are similar. The laboratory head will then choose appropriate methods which express the similarity between samples. Once the questions and procedures are chosen everything depends on the integrity of the sample. If they have been collected with care and documented amply then the results from the laboratory can be trusted (Steck, 2004).

Conclusion:

Take samples of all the soil in and around a crime scene. Place a reference sample in a plastic vial and label it with the date the time the investigators name and the case number. Reference samples are samples of soil from places the suspect or victim may have picked up soil. The reference sample can also be from sites the suspect may have been. Include the location and the distance from the focal point of the crime when labeling samples.

Reference samples should be about a tablespoon or so taken from less than a 1/2 an inch (about 1 cm). The exception is in cases of burial where samples should be taken every 1 inch (every 3cm). With gravesites the bottom of the grave should be sampled after the removal of the remains. Package and label all samples carefully. Keep in mind that the analysts in the laboratory do not have firsthand knowledge of the scene and the circumstances of collection. Try to provide a detailed description of the scene and the circumstances of the crime which the laboratory staff can use to determine what type of analysis is most appropriate.

Package all movable objects such as clothing, footwear and tools intact and protected from jostling.

Source: www.crimeandclues.com

Forensic Paint Analysis and Comparison Guidelines:

This document is intended to be a suggested revision to the original ASTM E1610-94 Guide. This revision is the product of the Paint Subgroup of the Scientific Working Group for Materials Analysis (SWGMAT). Its ultimate acceptance as an ASTM document will be the responsibility of ASTM Committee E-30 on Forensic Sciences. You are invited to submit constructive feedback on the Document Comments Form.

1.0. Scope

1.1. Forensic paint analyses and comparisons are typically distinguished by sample size that precludes the application of many standard industrial paint analysis procedures or protocols. The forensic paint examiner must address concerns such as the issues of a case or investigation, sample size, complexity and condition, environmental effects, and collection methods. These factors require that the forensic paint examiner must choose test methods, sample preparation schemes, test sequence, and degree of sample alteration and consumption suitable to each specific case.

1.2. This document is an introduction for the forensic examination of paints and coatings. It is intended to assist personnel who conduct forensic paint analyses in the evaluation, selection, and application of tests that may be of value to the investigation. The guidelines that follow describe methods to develop discriminatory information using an efficient and reasonable order of testing. The need for validated methods and quality assurance guidelines is also addressed. This document is not intended to be a detailed methods description or rigid scheme for the analysis and comparison of paints but a guide to the strengths and limitations of each analytical method. The goal is to provide a consistent approach to forensic paint analysis.

1.3. Some of the methods discussed in these guidelines involve the use of dangerous chemicals, temperatures, and radiation sources. This document does not address the possible safety hazards or precautions associated with its application. It is the responsibility of the user of these guidelines to establish appropriate safety and health practices and to determine the applicability of regulatory limitations prior to use.

2.0. Reference Documents

2.1. ASTM D16 Terminology Relating to Paint, Varnish, Lacquer, and Related Products¹

2.2. ASTM D1535 Method for Specifying Color by Munsell System

2.3. ASTM E308 Test Method for Computing the Colors of Objects by Using the CIE System

2.4. ASTM E1492 Practice for Receiving, Documenting, Storing, and Retrieving Evidence in a Forensic Science Laboratory²

3.0. Terminology

3.1. For definitions of terms used in these guidelines other than those listed, see ASTM D16 Terminology Relating to Paint, Varnish, Lacquer, and Related Products.¹

3.2. Descriptions of Terms Specific to this Guide:

3.2.1. Binder: A nonvolatile portion of the liquid vehicle of a coating, which serves to bind or cement the pigment particles together.

3.2.2. Coating: A generic term for paint, lacquer, enamel, or other liquid or liquefiable material that is converted to a solid, protective, or decorative film or a combination of these types of films after application.

3.2.3. Discriminate: To distinguish between two samples on the basis of significant differences; to differentiate.

3.2.4. Discriminating Power: The ability of an analytical procedure to distinguish between two items of different origin.

3.2.5. Known Sample: A coating sample of established origin.

3.2.6. Paint: Commonly known as a pigmented coating.

3.2.7. Pigment: A finely ground, inorganic or organic, insoluble, and dispersed particle. Besides color, a pigment may provide many of the essential properties of paint such as opacity, hardness, durability, and corrosion resistance. The term pigment includes extenders.

3.2.8. Questioned Sample: A coating sample whose original source is unknown.

3.2.9. Significant Difference: A difference between two samples that indicates that the two samples do not have a common origin.

3.2.10. Additive (modifier): Any substance added in a small quantity to improve properties. Additives may include substances such as driers, corrosion inhibitors, catalysts, ultraviolet absorbers, and plasticizers.

4.0. Quality Assurance Considerations

4.1. A quality assurance program must ensure that analytical testing procedures and reporting of results are monitored by proficiency tests and technical audits. General quality assurance guidelines may be found in Trace Evidence Quality Assurance Guidelines (1).

5.0. Summary of Practice

5.1. Physical and Chemical Features
Paint films are characterized by a number of physical and chemical features. The physical characteristics may include color, layer sequence and thickness, surface and layer features, contaminants, and weathering. Chemical components may include pigments, polymers, and additives. These features can be determined and evaluated by a variety of macroscopical, microscopical, chemical, and instrumental methods. Limited sample size and sample preservation requirements mandate that these methods be selected and applied in a reasonable sequence to maximize the discriminating power of the analytical scheme.

5.2. Questioned and Known Samples
Searching for differences between questioned and known samples is the basic thrust of forensic paint analysis and comparison. However, differences in appearance, layer sequence, size, shape, thickness, or some other physical or chemical feature can exist even in samples known to be from the same source. A forensic paint examiner's goal is to assess the significance of any observed differences. The absence of significant differences at the conclusion of an analysis suggests that the paint samples could have a common origin. The strength of such an interpretation is a function of either or both the type or number of corresponding features.

5.3. Motor Vehicle Identification
An important aspect of forensic paint analysis is the identification of the possible makes, models, and years of manufacture of motor vehicles from paint collected at the scene of a crime or an accident. The color comparison and chemical analysis of the undercoat and topcoat systems requires a knowledge of paint formulations and processes, collections of paint standards, and databases of color and composition information.

5.4. Sample Documentation
The test procedure selected in a paint analysis and comparison begins with thorough sample documentation. Some features of that documentation are described in ASTM E1492 Practice for Receiving, Documenting, Storing, and Retrieving Evidence in a Forensic Science Laboratory.² Analysis generally begins with appropriate nondestructive tests. If the initial tests are inconclusive or not exclusionary, the examination may proceed with additional tests that are selected on the basis of their potential for use in evaluating or discriminating the samples of interest or both.

6.0. Significance and Use

6.1. These guidelines are designed to assist the forensic paint examiner in selecting and organizing an analytical scheme for identifying and comparing paints and coatings. The size and condition of the sample or samples will influence the selected analytical scheme.

7.0. Collection of Suitable Samples

7.1. The potential for physical matches between known and questioned samples must be considered before selecting the method of paint sample collection. Care should be taken to preserve the potential for a physical match.

7.2. Questioned Samples
7.2.1. Questioned samples should include all loose or transferred paint materials. Sources of questioned samples can include tools, floors, walls, glass fragments, hair, fingernails, roadways, adjacent structures, transfers or smears on vehicles, or transfers to or from individuals such as damaged fabric with paint inclusions. Items with paint transfers should be appropriately packaged and submitted in their entirety for examination whenever possible. If sampling is necessary, the procedures listed in Trace Evidence Recovery Guidelines (2) may be used. When paint evidence is recognized, every effort should be made to manually remove it before using tape lifts to collect other types of evidence. If paint is collected with tape lifts, be aware of the possible difficulty encountered when attempting to manipulate paint samples bearing adhesive residues. In addition, components of the adhesive could contaminate the paint sample and change its apparent chemistry.

7.2.2. Smeared transfers can exhibit mingling of components from several layers or films that could preclude application of some of the analytical methods discussed in these guidelines. Because of the difficulties associated with collecting smeared or abraded samples, the entire object bearing the questioned paint should be submitted to the laboratory whenever possible.

7.2.3. When contact between two coated surfaces is indicated, the possibility of cross transfers must be considered. Therefore, if available, samples from both surfaces should be collected.

7.3. Known Samples
7.3.1. When feasible, known paint samples must be collected from areas as close as possible to, but not within, the point or points of damage or transfer. These damaged areas are usually not suitable sources of known samples. The collected known samples should contain all layers of the undamaged paint film. Substantial variations in thickness and layer sequences over short distances can exist across a painted surface. This is particularly true in architectural paint and automotive films where the curves, corners, and edges are often impact points and may have been subjected to previous damage, sanding, or overpainting. If necessary, several known paint samples should be taken to represent all damaged areas. Known paint samples collected from different areas should be packaged separately and labeled appropriately.

7.3.2. The surface underlying the suspected transfer area should be included for analysis when possible. Adjacent sections removed from a wall, ceiling, door, window, implement handle, and automobile door, fender, and hood are examples of items that can be valuable for assessing questioned and known sample differences and for evaluating the possible cross transfer of trace materials.

7.3.3. Paint flakes can be removed from the parent surface by a number of methods. These include but are not limited to the following: lifting or prying loosely attached flakes, cutting samples of the entire paint layer structure using a clean knife or blade, or dislodging by gently impacting the opposite side of the painted surface. When cutting, it is important that the blade be inserted down to the parent surface. It should be noted that no one method of sampling should be relied upon exclusively.

Source: www.fbi.gov

Paint Analysis

[The entire page is 891 words long]

Glass Analysis - "Seeing through glass":

Article taken from Issue 2 of the Forensic Access Newsletter "Benchmark"

TAs a type of evidence glass can be very useful contact trace material in a wide range of offences including burglaries and robberies, hit-and-run accidents, murders, assaults, ram-raids, criminal damage and thefts of and from motor vehicles. All of these offer the potential for glass fragments to be transferred from anything made of glass which breaks, to whoever or whatever was responsible. Variation in manufacture of glass allows considerable discrimination even with tiny fragments.

Information from the Forensic Science Service indicated that 60% of cases involving glass provided some positive evidence and that in 40% of these cases this evidence was strong. Depending on circumstances, the findings can also refute the allegation that a person was involved in a crime.

For example, when a pane of glass is broken, minute glass fragments can be showered onto the hair, clothing and footwear of people in close proximity - at least 1.5 and possibly up to 3 metres away. The number of fragments transferred decreases rapidly with distance from the breaking pane. Aside from backwards projection of fragments towards the 'breaker', fragments can also be acquired, for example, by climbing through a broken window or treading on pieces of broken glass.

Fragments recovered from hair and clothing are generally in the range 0.25 - 1 millimetre (1mm = 0.039"). Most glass is lost fairly rapidly - depending on the activity of the wearer and the texture of their clothing. For example, a woollen jumper will tend to retain glass fragments for far longer than a leather jacket, although fragments can be trapped in pockets, in crevices on shoe uppers and remain embedded in shoe soles for long periods of time.

The results of surveys of the numbers and types of glass fragments found on the clothing of people selected at random shows that it is unusual to find more than a few fragments of glass from the same source on someone's clothing purely by chance.

Discriminating between different glasses
By and large forensic scientists are interested only in freshly broken glass (clean and sharp-edged fragments) recovered from hair combings or the surfaces of garments, i.e. glass which could have been broken and/or acquired recently. These will be compared and contrasted with reference samples of broken glass, e.g. from the scene, by way of refractive index measurements (a measure of the degree to which the glass bends light) and chemical analysis tests. Refractive Index (RI) is a very accurate test which can distinguish between a large number of different glasses. If the recovered fragments differ in refractive index from a reference glass sample, then they could not have originated from the same piece of glass. Chemical analysis provides detailed information about the chemical constituents of the glass i.e. from the sand and other materials used in its manufacture. Chemical analysis can be used to distinguish between glass samples which have the same refractive index but different chemical composition, and recent advances in the application of analytical techniques in our laboratories continue to increase the discriminating power of this approach.

In addition, the surfaces of glass fragments will be microscopically examined for evidence of the method of manufacture and the type of object from which they came, for example, flat glass and patterned glass (both from window panes) or curved glass (drinking glass or bottle). Further tests may be performed to see if the source was of toughened glass (forming small cubes when broken and typically found in some car windows and in door and window glazing).

Interpreting what's found
If the recovered fragments match the reference sample both in RI and chemical composition it is necessary then to discover how rare or otherwise the glass might be. To do this the scientist may consult a computer database containing the combined results of the RI measurements and the chemical analysts results for each and every reference glass sample examined by his lab. This will show how many times a particular type of glass has been encountered, but this is not necessarily a reliable indication of how common it might be. This is because most glass samples submitted to forensic laboratories are from broken windows, although research has shown that glass found on clothing by chance is more likely to have originated from a container (such as a glass or a bottle). Aside from this, there tend to be local pockets of specific types of glass, e.g. from buildings all built at the same time. All this means that information held on the database might be skewed and should be treated with caution.

Aside from databases, the forensic scientist will also need to consider for example, the number and distribution of the glass fragments he has recovered and whether this fits in with the alleged circumstances.

The finding of numerous fragments of glass on a suspect detained within a few hours of windows being broken may be very strong evidence, for example if the glass is unusual and/or there is more than one type of matching glass. On the other hand, less weight would be given to the presence of one or two fragments of a common type of glass found on clothing seized several days after an incident.

Finally, it is often suggested that fragments might be transferred between people who come into contact after the crime has been committed, for example when they travelled side-by-side in a police vehicle. Whilst in theory this is quite conceivable, the results of tests show that only one or two fragments at most are likely to be transferred in this way and only a few remain on the seat occupied by the contaminated person.

Source: www.forensic-access.co.uk

ALL THE COLORS OF THE RAINBOW - FORENSIC PAINT ANALYSIS:

Go To Page: 2

Toolmark Identification:

Firearms examiners also conduct analyses dealing with toolmark identification, which involves the identification of a toolmark as having been produced by a particular tool. Though a tool can be thought of as the harder of two objects used to mark the softer object, a toolmark examination refers specifically to the analysis of an object used to gain a mechanical advantage (a more common definition of tool) and the objects bearing toolmarks or impressions from such use.

As with the identification of firearms, the examination of tools and evidence bearing the marks of tools is based upon observable class and individual characteristics. Pliers and screwdrivers, for instance, can be eliminated as having produced certain toolmarks if those impressions are significantly larger or smaller than the width of the tools' grasping jaws or blades. Like the size and shape of a tool's working surface, the distance between a toothed instrument's teeth is considered a class characteristic. Individual characteristics, produced during manufacture and use, are unique to a particular tool or toolmark but can include noticeable defects such as missing or partial teeth, raised metal nodes or ridges, distinctive signs of wear or damage, or a broken tip or blade.
	Associated tool, wires, and plates in a toolmark case
	Spacing between teeth in gripping or cutting instruments can play a major role in forensic toolmark examinations

The conclusions reached by examiners analyzing toolmarked evidence are the same as those reached in firearms examinations: identification, exclusion, and no conclusion. With regard to tools, an identification signifies a match between two toolmarks or a match between a tool and evidence bearing toolmarks; a nonidentification denotes a lack of association between two items of evidence—the possibility that a tool produced a given mark or that two marks were produced by the same tool is excluded. No conclusion, as in the examination of firearms-related evidence, indicates insufficient corresponding microscopic characteristics and the consequent inability of the examiner to classify the evidence as either an identification or an exclusion.

Additional information on the forensic examination and identification of tools and toolmarks is available in the Toolmarks Examinations section of the Handbook of Forensic Services.

Disposition of Evidence

Before examiners conduct any of the specialized microscopic examinations involved in the identification of firearms and toolmarks, evidence submitted to the FTU is subject to preliminary processing. Physical science technicians are responsible for the inventory of incoming evidence and must verify that all items described by a contributor as having been sent to the Laboratory have actually arrived. FTU technicians label each piece of evidence as either a Q or a K, with Qs referring to questioned items and Ks denoting known specimens. Bullets, cartridge cases, shotshell casings, and other ammunition components are given Qs; firearms and tools are given Ks. All submitted items are individually marked with the appropriate Laboratory Number and listed on a worksheet that is maintained with the evidence for the duration of the case examination.

Evidence that must be examined by other units in the Laboratory prior to being examined in the Firearms-Toolmarks Unit is separated and distributed by the technician to those units as needed. When evidence does not require examinations other than those conducted by the FTU, the technician may begin preparing the submitted items for analysis following general case inventory. This preparatory handling may entail weighing and photographing specimens, researching printed literature on specific firearms and ammunition, writing notes on individual Qs and Ks, and microscopically measuring the general rifling characteristics of bullets—caliber, number of lands and grooves, and their direction of twist (right or left). Measurements of the latter defining features are made for known, test-fired specimens as well as for questioned bullets and can be compared to specimens in the General Rifling Characteristics (GRC) File, a computer database used to generate lists of firearms that could have produced such markings on fired ammunition.

Firearms and other evidence recovered from crime scenes and field investigations are shipped to the FBI Laboratory and inventoried by technicians in the Firearms-Toolmarks Unit. Submitted firearms are marked as known specimens, or Ks; cartridges and other ammunition components of unknown origin are marked with Qs.

Reference Collections and Databases

Known bullet and cartridge case specimens generated through water tank test firing are maintained in the Reference Fired Specimen File of the Firearms-Toolmarks Unit following case completion for future comparison purposes. During the course of FTU casework, technicians may also enter the serial numbers of questioned firearms into the FBI's National Crime Information Center (NCIC) database, where they are checked against lists of serial numbers from weapons registered as being stolen.

The Reference Firearms Collection (RFC) contains over 5,100 handguns and shoulder firearms and is an invaluable reference in the identification of evidence firearms and firearms components, which can be matched against cataloged, intact collection specimens. Firearms in the collection are referenced for the locations of serial numbers and other identifying characteristics that assist in the classification of submitted weapons. The RFC also provides a supply of working parts for test-firing purposes in those instances when a firearm submitted as evidence has inoperable or missing parts and cannot be test fired in its received condition. In addition, firearms shown in bank robbery surveillance films can be compared with models from the RFC and potentially identified.

The Reference Firearms Collection

The Standard Ammunition File (SAF) is a collection of over 15,000 military and commercial ammunition specimens of foreign and domestic manufacture. These specimens include whole as well as disassembled cartridges for each ammunition type and serve as standards in the identification of intact evidence as well as miscellaneous disassociated shot wads, pellets, shot cups, bullets, cartridge cases, and shotshell cases. A computer database was recently created for the information in this file, allowing comprehensive searches to be conducted on submitted ammunition components based on physical features.

Examples of the disassembled cartridge and shotshell specimens maintained in the Firearms-Toolmarks Unit's Standard Ammunition File, which facilitate the identification of ammunition components submitted as evidence

The DRUGFIRE database allows examiners across the country to compare and link evidence obtained in the course of serial shooting investigations, especially those involving gangs and drugs. After test firing a weapon submitted as case evidence, FTU personnel can digitally capture and store images of bullets and cartridge cases using the DRUGFIRE system. These images can be compared to thousands of other images of bullets and cartridge cases entered by category and classification into the database by DRUGFIRE operators throughout the country. Hits are made when a system user finds a match between a specimen he or she added into the database and a previously filed specimen. With DRUGFIRE imaging, crimes committed in one locale can be tied to crimes committed elsewhere, and laboratories in many areas can access valuable forensic data.

Per agreement between the FBI and the Bureau of Alcohol, Tobacco and Firearms, all DRUGFIRE systems used in state and federal law enforcement will gradually be replaced with the National Integrated Ballistics Information Network (NIBIN). The NIBIN system will perform the same functions as DRUGFIRE and is expected to be fully operational within the next two years.

Continue—Part 3 Source: www.fbi.gov

Additional Articles in Identification Evidence.......