Forensic Chemistry & Trace Evidence

Trace evidence is a type of physical evidence, explained by the Federal Bureau of Investigation (FBI) as “trace materials that could be transferred during the commission of a violent crime.”[1] Trace evidence can be analyzed both physically and chemically, which is traditionally conducted by a forensic chemist. Forensic Chemistry is a large area of forensic science which may include illicit drugs, fiber analysis, explosive analysis, gunshot residue, fire debris, and more. For example, physical characteristics of a nylon fiber may be observed by microscope, and chemical analysis of the dyes in the fiber may be performed using an instrument called a Fourier transform infrared spectrometer (FTIR.) Both methods are useful when determining the unique characteristics of a particular fiber. Chemistry and trace evidence serve to connect a suspect to a crime scene, a suspect to a victim, or a victim to a crime scene. Matching of an unknown sample from the crime scene and known sample in chemical and trace analysis is primarily based on comparing instrumental analytical data. Some types of evidence that fall into trace evidence and chemistry include: hairs, fibers, soil, glass, controlled substances/drugs, lubricants, inks/dyes/paints, explosives, and fire debris. Toxicology may also be included in this category, because it is the chemical analysis of biological samples to detect trace levels of illicit drugs and their metabolites.

Refer to chapter 5 of the 2009 NAS report on forensic science for further descriptions of disciplines: controlled substances, hair, fiber, paint and coatings, or explosive evidence, and fire debris.[2]

Resources

Drug chemists identify controlled substances and other chemicals. The NIST Webbook is an excellent resource for checking such analysis.
As part of its Forensic Science Assessments: A Quality and Gap Analysis, the American Association for the Advancement of Science (AAAS) released a report on Fire Investigation.
Pills are commonly presented as evidence in criminal cases. Drugs.com is a good resource for researching pill markings.
Clandestine laboratories manufacture many tablets that contain controlled substances. While far less reliable due to the nature of clandestine labs, ecstasydata.org attempts to educate the public as to the contents of these clandestine tablets.
Designer drug manufactures has increased dramatically in recent years. Cayman Chemical is a commonly used source for standards of these new and emerging drugs.
The National Institute of Justice commissioned a study of color tests and the substances they will test positive with.
Forendex is a website created by the Southern Association of Forensic Scientists. It’s a good resource for controlled substance research.
The Nation Fire Protection Association (NFPA) publishes standards that fire investigators adhere to. Copies of the NFPA 921 and 1033 can be found here.
Gun shot residue (GSR) is occasionally used to show that a person was in the presence of gun shot residue. A more comprehensive overview of GSR can be found at the Scientific Working Group for Gunshot Residue (SWGGSR) website.
The Organization of Scientific Area Committees for Forensic Science (OSAC) is in the process of reexamining the guidance documents used by trace evidence analysts. The Trace Evidence Subcommittee is a good resource for these guidance documents.

Reviews of Current Trends in Forensic Science

Forensic science is a constantly progressing field due to the advent of new instruments, techniques, and novel interpretations. Considering the evolving nature of the discipline, it is imperative that legal professionals and scientists remain aware of modern methods and advancements in forensic science. Emily Lennert with the UCF National Center for Forensic Science regularly reviews journal articles related to forensic science. Those reviews can be found here with the accompanying citation to the journal article for further reading.