The evolving skills and knowledge of the pathologist, who examines the corpse; the chemist and toxicologist, who analyze bloodstains and traces of poisons; the ballistic expert, who deals with guns and ammunition; and others who play a role in helping police secure a conviction are described. Prominent figures in the history of forensic science are shown advancing their skills in a number of infamous and historically important criminal cases. Specific topics focus on Alphonse Bertillon's now discredited system of identifying criminals through physical measurements (anthropometry), which forms the basis of modern identification techniques, as well as Soviet Professor Gerasimon's skull reconstructions and other forensic work. The principle behind all forensic science cases is that a criminal always leaves something at the scene of the crime and always takes something away with him (e.g., a murderer may leave a body and take away a splash of the victim's blood). Forensic evidence is used not only to convict the guilty but also to clear the innocent. For example, in the 1954 Ohio case in which Dr. Sam Sheppard was convicted of murdering his wife, Sheppard contended that he himself had been attacked by the assailant when attempting to prevent the assailant's escape. Based on inaccurate forensic interpretation and testing by the county coroner, Sheppard was convicted. This conviction was reversed on appeal 12 years later when proper analysis and testing revealed blood stains inside Dr. Sheppard's wristwatch, indicating that it must have been removed by the assailant after the attack. Other forensic evidence proved conclusively that Dr. Sheppard could not have been the murderer. Forensic science as a regular, practical discipline is less than 100 years old. Nevertheless, today it is a vital aspect in crime solving. In 1978, the 7 British regional forensic science laboratories dealt with over 50,000 major criminal cases and achieved success in almost all of them. The evidence of scientists is becoming increasingly important as juries become more reluctant to convict on the evidence of police officers alone or on the unsupported testimony of identification evidence. Photographs and index are included.