This post originally appeared on the Trace.
In the United States, deliberate killing of police officers is relatively rare. Since 2000, according to FBI statistics, 791 police officers have been murdered on the job—an average of 55 killings each year. The ambush in Dallas on Thursday night, which killed five police officers, amounted to the deadliest attack on law enforcement since 9/11, when 71 officers died in New York.
Even so, police are far more likely to die in a fatal attack than the average worker. In 2013, according to an analysis by the Washington Post, only cab drivers were more likely to be murdered on the job. As of Friday morning, 26 officers have died in firearm-related incidents in the US this year, an increase of 44 percent over the same period in 2015, according to the National Law Enforcement Officers Memorial Fund.
Looking back over the past 100 years, the Trace found that there have been at least 11 attacks that left four or more law enforcement officials dead.
July 7, 2016: Five police officers, including one transit officer, died in the Dallas sniper shooting. Another seven officers were also struck by bullets, as were two civilians, including a woman who was hit as she shielded her children.
November 29, 2009: Four officers were gunned down in a suburban Seattle coffee shop. The shooter, a career criminal, was killed two days later during a standoff with a Washington police officer.
March 21, 2009: Two motorcycle officers were shot and killed in East Oakland, California, following a traffic stop. Two hours later, the gunman, a convicted felon wanted for a parole violation, fatally shot two members of a SWAT team that had tracked him to a nearby apartment building.
September 11, 2001: Seventy-one officers died while responding to the attacks on the World Trade Center in lower Manhattan. A US Fish and Wildlife officer was also killed that day in the United Flight 93 crash outside of Shanksville, Pennsylvania. He was believed to be one of the passengers who attempted to retake the plane from terrorists before it crashed.
April 19, 1995: Eight federal law enforcement officials died in the terrorist bombing of the Alfred P. Murrah Federal Building in Oklahoma City.
February 28, 1993: Four agents with the US Bureau of Alcohol, Tobacco, Firearms, and Explosives were killed during a firefight as they tried to execute a search warrant at the Branch Davidian compound in Waco, Texas.
December 31, 1972 to January 7, 1973: Over an eight-day period, a sniper gunned down five law enforcement officers in New Orleans before he was killed while hiding in a hotel. The shooter had developed an intense hatred for police after joining the Black Panthers.
April 6, 1970: Four California Highway Patrolmen were killed in two separate shootouts with a pair of heavily armed criminals in northern Los Angeles County. Known as the Newhall Incident, the shooting led to a nationwide shift in police survival training.
October 30, 1950: Eight officers were shot and killed during a political revolt in Puerto Rico aimed at overthrowing the first republican government in the island territory, which had just been approved by Congress.
January 2, 1932: Six officers were fatally shot as they tried to apprehend two men wanted for murder at a farm in southwest Missouri.
November 24, 1917: Nine officers were killed in a bomb blast at a police station in Milwaukee, Wisconsin. An investigation later linked the bombing to a group of Italian anarchists, who had delivered a package containing the device to an evangelical church. Finding the package suspicious, the church handed it over to police, and it subsequently exploded. It remained the deadliest single incident in US law enforcement history until 9/11.