"The recent shooting deaths of police officers in Dallas, TX, and Baton Rouge, LA, have served as a reminder of the danger law enforcement officers can face while serving the public. While these attacks have heightened attention on deaths suffered by police officers in the line of duty, data indicate that the number of law enforcement officers killed in the line of duty has generally decreased over the past three decades. However, the number of officers killed in ambush situations has remained fairly steady. Annually, on average, nine law enforcement officers have died in ambush situations between 1979 and 2014."
CRS Insight, IN10527
Federation of American Scientists: http://www.fas.org/sgp/crs/index.html