The My Lai Massacre was an atrocity that was committed during the Vietnam War. It happened in March of 1968. The soldiers who committed this atrocity were Americans.
The only person who was actually convicted of and punished for participating in the My Lai Massacre was Lt. William Calley. He was the commander of the platoon that committed the atrocity.
In this atrocity, hundreds of Vietnamese civilians were killed. Many of them were attacked in other ways. There were, for example, rapes as well as evidence of beating and torture.
This atrocity helped to turn public opinion in the US even further against the war.