The central aim of the study was to determine whether there has been any change over time in either the characteristics of victims or the circumstances of homicide incidents within the prison environment. The study's definition of inmate murder was 'the killing of a Federal penitentiary inmate within the penitentiary walls or perimeter of the grounds. The killing may be intentional or accidental, with or without justification.' Data on victims and incident circumstances were obtained from institutional files and security incident reports. The findings suggest the incidence of prison homicides has increased over the years, and the character of victims and victimizations has changed. More recent prison homicides were more likely to have been carried out by multiple assailants, were more commonly associated with revenge motives or drug and gambling debts, and victims were more likely to have violent backgrounds. The study concludes that more complete understanding of the causes of prison homicides will require detailed analysis of the process of conflict escalation in these settings. 1 figure, 4 tables, and 16 references. (Author abstract modified)