William Calley, who as an Army lieutenant who during the Vietnam War carried out one of the worst war crimes in U.S. military history, died in April, according to news reports Monday. He was 80.

The Washington Post, which first reported the death, cited a death certificate. 

The New York Times also reported the death, citing Social Security Administration records. 

Neither paper gave a cause of death. Calls to numbers listed for Calley’s son, William L. Calley III, were not returned, Reuters reported.

Calley led his U.S. Army platoon into the Vietnamese hamlet of My Lai. The soldiers killed 504 people on March 16, 1968, in Son My, a group of hamlets between the central Vietnamese coast and a ridge of mountains, in an incident known in the West as the My Lai Massacre, according to The Telegraph. The killings galvanized the anti-war movement.

Calley was Initially charged in a U.S. Army court martial for 102 deaths, He was sentenced to life in prison in 1971 for the killing of 22 civilians. Then-President Richard Nixon ordered he be released under house arrest, The Telegraph also reports.