Data in the report were derived from three sources: for 1980-84, a 1985 mail and telephone survey that had a 93-percent response rate; for 1970-74, unpublished police department reports to the FBI on their justifiable homicides; and for 1975-79, a survey conducted by the International Association of Chiefs of Police. According to the report, at least 353 citizens were killed by police in 50 cities in 1971, but only 172 were killed in 1984. Citizen killings of police in these cities fell by two-thirds in the same 15-year period. Homicide and violence in general, however, did not decline. Much of the decline in police killings of citizens consisted of reduced killings of blacks. The best explanation of these trends is increased pressure on police to use their guns less freely, imposed by progressive police chiefs and civil litigation. Cities vary widely in the percentage of all homicides committed by police and in the rate of citizens killed per 100,000 population. The report discusses the quality of the data and comments on the need for standard definitions and a national reporting system. Tables and 19 references. (Author summary modified)