I believe what you are interested in defining is forensic chemistry or the use of chemistry for legal purposes, such as crime scene investigations. Forensic chemistry can include looking at trace evidence such as collecting hairs, glass, soil, paper, and gunshot residue or running toxicology screens to look for drugs or other substances in the body or conducting DNA testing. One of the unique challenges that forensic chemists face is the fact that they may not know the nature of the sample that they are processing and have to use a number of scientific techniques and testing to examine and identify the evidence such as microscopy, spot testing, and mass spectrometry to name a few. A forensic chemist is often called to provide expert testimony and provide evidence to the jury. Forensic chemistry has become a very popular career recently due to television shows such as "Bones," "CSI," and "Dexter."
Chemistry in criminology for me is the use of lab tests, chemicals and equipment to analyse physical and forensic evidence. Also the use of chemicals to assist in the production of evidence to a court or jury.
Chemistry in criminology doesn't necessarily have a set in stone definition. Chemistry is the basis for the analysis of the crime scenes. Criminalists examine physical evidence to reconstruct a crime scene. Physical evidence can be saliva ,tears,semen ,a weapon, a piece of clothing, a bloodstain or drugs. Fingerprints, bullets and shoe impressions are some of the important clues that criminalists analyze to ascertain the crime.In this technique DNA will be isolated from blood stains,semen stains or hair roots and will be subjected to southern blotting and DNA hybridization with the help of specific DNA probes.