The mass shooting in Dallas that left five officers dead and six others wounded is the deadliest attack on law enforcement since 9/11, according to statistics from the National Law Enforcement Officers Memorial Fund.

Dallas Police have confirmed that four of their police officers have died, and Dallas AreaRapid Transit (DART) has confirmed that one DART officer also died. DART has identified him as Officer Brent Thompson, 43. He was the first DART officer to be killed in the line of duty since the agency’s formation.

The deadliest day for U.S. law enforcement in history was 9/11, in which 71 officers died while responding to the terror attacks on the World Trade Center in Lower Manhattan — including 37 members of the Port Authority of New York and New Jersey Police Department, which represented the single largest loss of law enforcement personnel by a single agency in U.S. history, according to the Fund.

11 Officers Shot, 5 Fatally, by Snipers Amid Dallas Protest; Standoff Underway

First of the Officers Killed in Dallas Identified

President Obama Describes Dallas Shootings As ‘Vicious, Calculated, Despicable Attack’

Other deadly incidents for law enforcement include a sniper attack in New Orleans in the 1970s.

Over a period of eight days in 1972-1973, five officers were killed by a sniper in New Orleans. The gunman belonged to the Black Panthers. The shootings starting on New Year’s Eve and ended when the suspect was shot and killed by police, who used a Marine helicopter to fly over the hotel he was holed up in and fire at him.

Eight federal officers were killed in the Oklahoma City bombing in April 1995. Domesticterrorists, led by Timothy McVeigh, bombed the Alfred P. Murrah Federal Building – killing 168.