Since 1972 the California Specialized Training Institute has maintained detailed records of such murders. In addition to an examination of these records, interviews with surviving and investigating officers were conducted. During the 5-year period, 55 male police officers were murdered. According to the type of call, the leading killers of city police officers were robbery (eight officers) and disturbances (seven). Sheriffs' personnel died most often when answering calls reporting disturbances and suspicious persons or vehicles. Highway Patrol officers died most often while involved in traffic stops, transporting prisoners, and investigating drunk driver reports. The average age for the slain officers was 33.9 years, and the average length of law enforcement service was 8.4 years. By rank, 76 percent of the officers were patrol or deputy level officers, 11 percent were agents or detectives, and 9 percent were sergeants. Guns were used in 96 percent of the killings. The most lethal time period was 2100 to 2200 hours; other lethal times were 0300 to 0400, 0500 to 0600, 1300 to 1400, 1500 to 1600, and 1600 to 1700. Thursdays accounted for 22 percent of the slayings, Mondays and Saturdays for 16 percent each, Tuesdays and Fridays for 15 percent each, Wednesday for 11 percent, and Sunday for 5 percent. Fifteen percent of the murders occurred during August. Although no month was free of slayings, April, with only 4 percent, had the lowest total. Recommendations include a review of tactics for inservice training in the handling of disturbances, robberies, and suspicious persons or vehicles; and continual inservice training for all ranks. Footnotes and data tables are included.