A U.S. Army platoon commanded by Lt. William Calley forced unarmed Vietnamese into ditches and killed them. The platoon had taken several casualties and had poor discipline.
The massacre stopped when a U.S. helicopter, flown by Warrant Officer Hugh Thompson, landed and its crew physically intervened.
U.S. criminal process
He and his immediate superior Capt. Ernest Medina were both tried in military courts. Medina was found innocent, but Calley was found guilty and served four years in prison; his sentence of life imprisonment was commuted in 1975 by President Richard Nixon. The case became a focus of national guilt and self-doubt, with antiwar leaders alleging there were many atrocities that had been successfully covered up.