A forensic chemist is a scientist who typically will work for a law enforcement laboratory or private government agency. He or she identifies and analyzes physical evidence collected from crime scenes. Although a forensic chemist does not generally participate in the actual collection of evidence, he or she is a major part of the criminal investigative process. Forensic chemistry is a discipline that requires a vast array of knowledge, so a chemist may choose to specialize in blood typing, fingerprinting, chemical identification, or hair, soil, glass, and fiber analysis. Forensic chemists work all over the globe, including the United States, Australia, and the United Kingdom.
A forensic chemist who specializes in serology, the scientific study of blood typing and body fluids, uses enzyme tests on samples of semen, blood, saliva, hair, or other bodily fluids found at a crime scene. Since enzyme compounds found in fluid samples are almost always unique to a specific individual, the chemist can use the enzyme results to determine a unique DNA profile. Investigators can use that profile to find a suspect in a DNA database or to compare with possible suspects.
Evidence samples can be difficult to identify since they may be mixed with other substances, so a forensic chemist who specializes in chemical identification may have to use analytical techniques in order to separate the chemical compounds of a sample. Typically, he or she will use a gas chromatograph, an instrument that separates compounds from other impurities, like dust or dirt, in an evidence sample. A chemist can then make conclusions on what a sample is or where it came from, based on the chemical compounds that are extracted. For example, unidentified colored particles found on a victim’s body could be tested and found to be a particular brand and shade of paint. Investigators could then use that information to tie a suspect to the crime if the sample matches paint the suspect has in his house, for instance.
In addition to identifying and analyzing crime scene evidence, a forensic chemist may need to have mock trial courtoom experience as part of his or her job training since he or she will typically have to testify in criminal cases as an expert witness and present his or her conclusions on the evidence to the jury. Generally, he or she will compare the evidence with previous cases in order to give an expert opinion as to how that evidence specifically implicates a suspect. Although a forensic chemist will usually work in law enforcement laboratories, he or she must give unbiased, purely scientifically-based findings, even if the testimony works in favor of the defense.