Forensic science involves using scientific techniques for legal purposes, usually in a criminal investigation and trial. Forensic science is a highly technical field, involving chemistry, biology, physics metallurgy, and even engineering other fields that play a part include geology, psychology, and social science. Evidence, such as hair, fingerprints, or blood samples, is collected at the scene of the crime by forensic technicians. They try to match this eyidence to a suspect in the case, hopefully using a match to get a conviction. Then experienced forensic scientists, who often specialize in one forensic discipline, give the evidence in court as an expert witness.