The word Forensic comes from the Latin forensus, meaning of the forum. In ancient Rome, the forum was where lawmaking debates were held, but it was also where trials were held just like modern day courthouses. From that, forensic science has come to mean the application of the natural and physical science to the motion of matters within a legal context.

Forensic Science can be viewed as a tripartite structure consisting of a Collection, which pertains to the science investigation, Examination, which pertains to the medical investigation and, Presentation, which pertains to the courts. A forensic case will involve all aspects of each of the three structured elements, each being as important as the other. It is obvious that there needs to be a shared approach for the successful end of each case. Each step in forensic science must be done in an exact order; therefore it can be assured that the investigation can have few doubts about what is being debated.

The purpose of crime scene investigation is to help establish what happened at the crime and to identify the responsible person or people. Carefully documenting the situation at a crime scene and recognizing all-important physical evidence do this. The ability to recognize and properly collect physical evidence is often times vital to both solving and prosecuting violent crimes. It is no exaggeration to say that in the majority of cases, the law enforcement officer who protects and searches a crime scene plays a significant role in determining whether physical evidence will be used in solving or prosecuting violent crimes.

Documenting a crime scene and its conditions can include directly recording brief details such as lighting, furniture, fingerprints, and other valuable information. Certain evidence if not collected right away can easily be lost, destroyed or ruined. The range of investigations can also expand to the fact of dispute in such cases as suicide or self-defense. It is also important to be able to recognize what should be present at a crime scene, what to look for at a crime scene and what might appear out of place. A crime scene often does not relate to the direct area in which a victim or actual crime has occurred, but the possibility of escape or access routes should also be checked. Anything, which can be used to connect a victim to a suspect or a suspect to a victim or a crime scene, is important physical evidence. Richard Saferstein explains, Physical evidence encompasses any and all objects that can establish that a crime has been committed or can provide a link between a crime scene and its victim or a crime and its perpetrator.
One of the first things an officer should do once he gets to the crime scene is to take control and secure the scene as quickly as possible. This is to prevent anyone from ruining evidence and to keep unauthorized person or persons out of the area such as the media, the public or anyone who doesn't belong. While this is being done, an officer should also be alert for useless evidence and note if there are any possible approach or escape routes. After an officer does this, he should conclude the degree in which the scene has been protected and make sure there is enough security in the area. All persons entering and exiting the crime scene should be logged and kept down to a bare minimum to make sure the purity of the crime scene when the case goes to court. Each person involved in the crime scene should have knowledge relative to its original conditions to avoid from accidental movement of objects, evidence or anything, which might hurt in the investigation of the crime. When all of this is done, the next step that can occur is the actual inspection of the crime scene.

The inspection of the crime scene will usually begin with a walk through of the area along the trial of the crime. The trail is that area, which all noticeable actions connected with a crime, took place. It is also sometimes marked by the presence of physical evidence; this may include the point of entry, the location of the crime, areas where a suspect may have cleaned up and the point of exit. The purpose of the walk through is to note the location of potential evidence and to mentally outline how the scene will be physically examined. The first place investigators should look is the ground they walk on. This is to prevent any evidence from being destroyed and if observed should be marked and warned to others not to step in that area. As the walk through occurs, the investigators should make sure their hands are busy and they don't touch anything. The best way to prevent from touching anything is to keep your hands in your pockets. Once the walk through has been completed, the scene should be documented with videotape, photographs and sketches. Any or all objects can provide a link between a crime and its victim/suspect; therefore it is very important that the crime scene be well photographed and recorded One of the first steps in documenting and recording a crime is videotape. Videotapes can provide a perspective on the crime scene layout that cannot be as easily perceived in photographs and sketches. The condition of the scene should remain unmoved with the exception of markers placed by investigators to show small things that might not be seen such as bullets, bloodstains or other key pieces of evidence. A key in videotaping is slow movement through out the scene and should be done so from beginning to end. It is also wise to go over an area twice in order to prevent unnecessary rewinding of the tape when viewing and to make sure the taper has captured everything. Taping should begin with the general outline of the scene and surrounding area. Taping should continue throughout the scene using different angles, close-ups, and still shots for a few seconds. Once videotaping has finished it is then best to also capture the crime scene with still photography.

Regardless if a scene has been videotaped, still photographs are a must at every crime scene. Although videotaping does record everything, photographs can demonstrate certain things such as direct comparison. Actual size photographs can be used to compare fingerprint and shoe prints photographed at the scene against the suspect. Again, when photographing, the outer part of the scene should be taking first to show the surrounding areas, then towards the crime scene itself. Wide angle photos should be used of the crime scene and surrounding areas. A good technique to use when shooting rooms is to shoot from many possible angles such as from all four corners, from a doorway or from a window. When close-ups are necessary of key pieces of evidence, a ruler should be photographed with the items where relative size is important. While each photograph is being taken, a person should also be taking notes on what the person is shooting, in order at a later date to understand what was trying to be accomplished. After still photography has been taken, the final step in recording a crime scene is to sketch and draw the scene out by hand. While photographs are two-dimensional and often can alter distance and size, sketches provide the means of showing distance or objects, and an over-head view of the area and surroundings. A sketch is usually made of the scene as if one is looking straight down or straight ahead. Measurements should be taken at crime scene of distances between two objects, room measurements and key pieces of evidence. Two measurements should be taken at right angles to each other from two location points. Each measurement should be double measured to make sure they are correct and accurate. A professional using all the measurements and notes taken by the investigators can make a final sketch. However, the original sketches should not be thrown out but saved along with other key evidence in case a disagreement occurs or something was missed. Once the crime scene has been recorded with videotaping, still photography and sketches, gathering of evidence can occur.

Gathering and locating physical evidence is a very slow a tiresome job when done correctly, however, it can surrender many clues. One of the first things an investigator must determine is the size and area that must be searched. The main focus search must include all likely points of entry and exits used by the criminals. When searching, certain patterns may be used to cover and examine the area. There are about three different ways in which an area can be examined. One way is a spiral search method, which is by starting in the center of the scene and work in a spiral outward do this method until all of the scene has been covered and checked. Another method and usually the preferred method is the grid method. This is done by marking the crime scene into a grid and walking in a straight line from one side of the grid towards the other where as you make 180 degrees turn and come back a few steps over from where you just searched. This pattern overlaps itself and is one of the best search methods. The final method used is a quadrant or zone search. This is when the scene is divided into certain quadrants, usually four and each zone is searched with either the spiral or strip line search. Then after each zone is searched, the overall scene can be searched using the above patterns.
When evidence is found it must be package and protected in a way that prevents any physical change from happening from the time it is taken to the it reaches the crime laboratory. Such things like breakage, contamination, evaporation and ruined samples can all be avoided with proper handling and packaging. Original conditions must be maintained at all cost and when ever possible the entire object should be submitted to the crime laboratory. Good judgment must be maintained and common sense usually plays a role. Each different item must be placed in separate containers to prevent cross- contamination. It is also wise to take comparative samples, so that evidence can be compared to normal or controlled pieces.

 Unbreakable bottles with lids are good for such things as hair, glass, fibers and other evidence. However, when anything contains blood evidence, it must be placed in a non-seal able container, such as paper bags. This is to stop bacteria from forming and possibly making the evidence unusable. Also good for evidence collection are manila envelopes, cardboard boxes and paper bags. Besides blood, special interest must be made towards clothing. All clothing must be air-dried and placed individually in separate paper bags to ensure constant circulation to prevent mold or mildew from happening. The only time a seal able container must be used, is in the cases when suspicious fires are being investigated.

Finally, with gathering evidence at crime scenes, an investigator must make sure he not only labels the evidence, but also makes a correct description on all sketches and diagrams. Evidence should not be handled a great deal after recovery and should be kept down to as few people as possible. Investigators must continuously check paperwork, packaging notations, and other recording of information for possible conflict or errors, which may cause confusion or problems at a later time in court.
Once evidence is gathered it must be sent to a laboratory for processing and further investigation.