All persons accused of murder in Massachusetts are subjected to a 1- to 3-hour psychiatric interview to determine competency to stand trial or enter a plea. A preliminary review of 243 examinations of offenders performed between 1958 and 1978 by the Suffolk Superior Court Clinic showed that the single most common motive for murder was monetary gain. Because of a different approach employed in these examinations between November 1978 and October 1979, it was possible to obtain more complete data on the 31 murderers' motives and their relationships with the victim. Over 90 percent of these murders were committed by men, and monetary gain was the single most important motivating factor. In all but five cases, killer and victim knew each other as friends or acquaintances or were blood relatives. Many murders had occurred during illicit drug transactions involving heroin, cocaine, marijuana, hashish, and phencyclidine. Individuals who had killed in the course of armed robbery were generally established crooks or criminals. Murder was for sexual thrill in a few cases. The smallest proportion of murders was committed by the mentally ill. The paper provides several case histories and discusses the criminal justice system's failure either to protect society from perpetrators of serious crimes or to rehabilitate them. Tables are included. (Author summary modified)