Collecting Physical Evidence from Crime Scenes, Essay Example

The collection of physical evidence is often a significant component of a criminal investigation. Investigators gather all sorts of evidence, such as fingerprints, footprints, tire tracks, DNA, and innumerable other types of evidence. The manner in which such evidence is collected is important, as these evidence samples must be accurately gathered and meticulously maintained. There are numerous guidelines and methodologies involved in the gathering of physical evidence, and this essay will discuss several of them.

Foot prints left at crime scenes are often valuable tools for investigators. Foot prints can be used to determine the type of footwear a suspect was wearing, and can also provide other information, such as the size, weight, and actual activity of a suspect. Impressions of footprints are often taken in the form of casts; material such as “Ultracal 30” can be used to make these impressions.  In Great Britain, the Forensic Science Service has developed a nationwide database of footwear and footprints that allows investigators to quickly find information relevant to the footprint evidence gathered at crime scenes. Similar databases are maintained in the U.S. by the FBI and other organizations.

Another type of evidence that can be helpful in a criminal investigation is gunshot residue (GSR). When a firearm is discharged it releases gasses and particles that can be examined by investigators. There are two primary types of GSR: one is the material left on the individual who discharged the firearm; the other is the material deposited on the victim of the shooting. Investigators look for evidence of primer and other materials on the hands of the shooter; this material deteriorates fairly rapidly after the actual shooting, so it is important for investigators to collect such evidence as quickly as possible. Investigators should not allow the suspect to wash his or her hands until evidence can be collected, as the GSR can be easily washed away, rendering tests for it ineffective.

Investigators typically use a process called “adhesive disc sampling” to gather GSR evidence and they examine the GSR evidence with a scanning electron microscope (SEM). GSR offers investigators to not only determine if someone has fired a gun, but also to connect the GSR on the hands of a shooter to the specific gun that fired the shot. This is a valuable tool for investigators to help eliminate other suspects as well; while GSR can land on other people as well, the concentration is typically much higher on the hands of the shooter. Along with the GSR present on the hands of the shooter, a second type of GSR can be found on the target of the shooting. This material consists of burnt and unburnt gunpowder and other materials. This evidence is also useful for connecting a particular firearm to a shooting, and the patter of this type of GSR can also help to determine such things as the distance between the shooter and the target at the time of the shooting.

When collecting firearms and other related evidence from a crime scene, several factors must be considered. Above all else, safety is the primary concern when collecting firearms as evidence. There are several other important steps involved in gathering firearms and related evidence, all of which can be helpful in determining the facts of a case. The scene should be photographed and diagrammed, so as to determine the location of the shooter and target at the time of the shooting. Firearms can be collected while still loaded, though it is imperative that they be handled with the utmost care. It is important to preserve all available evidence, such as hair, blood, and fingerprints when collecting firearms.

When collecting evidence in various situations, there are often different techniques involved in doing so. When collecting a shoe print in dry dirt, for example, is is possible to make an impression of the print, but care must be taken to pour the casting medium very slowly and gently into the print. It is also imperative that prints be photographed, measured, and otherwise analyzed at the scene to insure all needed information has been gathered at the time, as the elements can quickly destroy the prints. Toolmarks left at entry points can also be helpful in matching a particular tool to a crime scene. Striations, scratches, and other indentifying characteristics of a tool can be examined microscopically to determine if a particular tool was used at a crime scene. By matching marks on the tools with impressions, and other damage left at a scene it is possible to further strengthen the identification of a particular tool with both the crime scene and the suspect. When possible, material at the scene containing toolmarks can be removed and taken to the lab; in other cases, rubber silicone and other materials can be used to make impressions of the marks for later examination. This holds true for such things as tire tracks as well; as is the case with shoe and foot prints, casts can be made at the scene, or material containing such impressions can be removed entirely for examination in the lab.

There are other means by which shoe prints and foot prints can be analyzed at the scene and in the laboratory. Shoe prints left on surfaces that cannot be cast for impressions can still be photographed; there are special techniques used in terms of lighting, types of film, and photographer angles that ensure the photographs will accurately capture the shoe print, denoting factors such as the size of the shoe. Electrostatic dustprint filters can be used to lift shoe prints found in dust on floors and other surfaces. Shoe prints found on tiles and other such surfaces can be maintained by actually removing the tile and taking it to the forensics lab.

These are just a few of the techniques and types of evidence that are used at crime scenes and in the forensics lab. Gathering evidence at the scene of a crime is a crucial first step in ay criminal investigation, and it is imperative that such evidence is properly handled and examined to ensure that it is well-preserved and useful in efforts to determine who committed the crimes and to effectively prosecute the offenders.

Resources:

http://www.forensicscienceresources.com/Shoes.htm

http://suite101.com/article/toolmarks-at-a-crime-scene-a41620

http://www.spsa-forensics.police.uk/services/chemistry/tool_marks

http://www.ctcase.org/bulletin/19_2/forensics.html

http://www.maine.gov/dps/msp/criminal_investigation/crimelab/latent.ht