Forensic Findings

We are all aware that reagent field tests are used a great deal by law enforcement. Reagent is defined as "a substance used in a chemical reaction to detect, measure, examine, or produce other substances" (www.answers.com/topic/reagent). Presumptive field tests are considered very reliable as evidence; however further testing may be required in a laboratory. There are field tests available for six different types of evidence. They include "blood, narcotics, impressions, fingerprints, trace, firearms and ammunition (www.associatedcontent.com/article/109258/how_to_detect_fingerprints_and_blood.htl).

Presumptive tests for blood are extremely common. Testing for blood is performed using a non destructive technique that will not interfere with subsequent laboratory testing. The most widely accepted field tests for blood involve three different chemical processes: phenolphthalein, leuco-malachite green, and luminal (www.leacorps.com/pdfs/Forensic_Supply_Products/12). I will go over luminal briefly. It is a "chemiluminescent substance that produces a bright green color when it comes into contact with the hemoglobin from blood" (www.leacorp.com/pdfs/Forensic_Supply_Products/12). It can be viewed under UV light in total darkness for a short period of time. Luminal can detect minute specks of blood that is old and/or has been cleaned.

Field tests for narcotics are used all the time. Once an officer finds drugs on a subject or in his/her possession (vehicle), the officer will test the drug on the scene within 5 minutes or less. Most tests are for a specific kind of drug. However, there are more modern kits that test for the presence of several different types. There is a multi-drug test panel device that tests for ten types of narcotics. Cocaine, methamphetamines, amphetamines, marijuana, THC, PCP, and opiates are just some of the drugs that are able to be tested. The substance will turn a color that is designed for a specific drug.

Reagents are frequently used to detect if a person has recently fired a gun. The detection can be made on the hands and/or clothing of a suspect. When a gun is fired, gunpowder residue and primer are blown back in the direction of the shooter's firing hand. Primer residue can normally be found on the web between the thumb and pointer finger as well as on the back of the hand that fired the weapon. A prepared spray bottle is used to spray the hand (http://faculty.ncwc.edu/toconnor/425/425lect06.htm). Trace metal detection on the skin and clothing is also used in the field. The Trace Metal Detection Technique (TMDT) makes "metal trace patterns visible on the clothing and/or skin that has been treated by a solution and then illuminated by an UV light source" (http://faculty.ncwc.edu/toconnor/425/425lect06.htm).

There are several methods used for the detection of latent fingerprints. Cyanaoacrylic (crazy glue) can be used to detect fingerprints on various surfaces including cars, guns, as well as bullet casings. Ninhyndrin is a chemical that bonds with amino acids in fingerprints. Ninhyndrin will produce a blue or purple color when it comes in contact with amino acids. This method allows for prints to be taken from cardboard and paper as well as other sources. Lastly, I will discuss the powders that are used a great deal on television and in real life to detect fingerprints. The powders adhere to both water and fatty acids of fingerprints and are usually utilized "on smooth surfaces" (www.associatedcontent.com/article/109258/how_to_detect_fingerprints_and_blood.html). Finally, either foot or tire impressions can be collected using dental casting.

Although I briefly went over some of the methods used for reagent testing, I believe it would be best for all to research this subject on your own. Anyhow, tests have to be documented in your case files. Some of the methods used to document are photography/video, sworn testimony, and written descriptions by witnesses to the tests.

Reference List:

Connor, T., (2006). "Firearms ID and ballistics". Retrieved February 6, 2007 from http://faculty.ncwc.edu/toconnor/425/425lect06.htm

LeaCorps Website, 2007. "Forensic Evidence: Analysis Equipment". Retrieved February 12, 2007 from http://www.leacorp.com/pdfs/Forensic_Supply_Products/12_forensicana.pdf

Jones, K., (2006). "How to detect fingerprints and blood". Retrieved February 12, 2007 from http://www.associatedcontent.com/article/109258/how_to_detect_fingerprints_and_blood.html

Answers Corporation Website, (2007). Retrieved February 13, 2007 from http://www.answers.com/topic/reagent