The field of forensic science is about using science for the purposes of the law, and therefore provides impartial scientific evidence for use in the courts of law, e.g. in a criminal investigation and trial. Forensic Science is a multidisciplinary subject, drawing principally from chemistry and biology, but also physics, geology, psychology and social science.
In criminal law cases, forensic scientists are involved in the examination of physical traces which may be useful for establishing or excluding a suspect of committing a crime. This evidence is gathered from the scene of the crime or the victim and is put through a series of tests to establish its relevance to the case.
These traces include blood and other body fluids, hairs, textile fibres from clothing, etc, materials used in buildings such as paint and glass, footwear, tool and tyre marks, flammable substances used to start fires and so on. Sometimes the scientist will visit the scene itself to advise about likely sequence of events, any indicators as to who the perpetrator might be, and to join in the initial search for evidence.