An Alaskan police officer found a woman's body while on routine patrol of a public park. The victim had been stabbed to death and, during the autopsy, the medical examiner preserved the portion of her rib cage which sustained the fatal wound. A knife thought to be the murder weapon turned up days later, two thousand miles away. Forensic scientists now had an opportunity, which seldom occurs: to compare the microscopic marks on the presumed murder weapon with the marks on the victim's bone.