That is easy to understand.
Lt. William Calley is convicted with six specifications of premeditated murder in the death of 109 Vietnamese civilians at My Lai in March 1968.
Calley, a platoon leader in Charlie Company, 1st Battalion, 20th Infantry, 11th Infantry Brigade (Light) of the 23rd (Americal) Division had led his men in a massacre of Vietnamese civilians, including women and children, at My Lai 4, a cluster of hamlets that made up Son My village in Son Tinh District in Quang Ngai Province in the coastal lowlands of I Corps Tactical Zone on March 16, 1968. The company had been conducting a search and destroy mission as part of the yearlong Operation Wheeler/Wallowa (November 1967 through November 1968). In search of the 48th Viet Cong (VC) Local Force Battalion, the unit entered Son My village but found only women, children, and old men. Frustrated by unanswered losses due to snipers and mines, the soldiers took out their anger on the villagers, indiscriminately shooting people as they ran from their huts and systematically rounding up the survivors, allegedly leading them to nearby ditch where they were executed.
This was terrible killing even it was in a war.
This incident was subsequently covered up, but eventually came to light a year later. An Army board of inquiry, headed by Lt. Gen. William Peers, investigated the massacre and produced a list of 30 persons who knew of the atrocity, but only 14, including Calley and his company commander, Captain Ernest Medina, were charged with crimes. All eventually had their charges dismissed or were acquitted by courts-martial except Calley, whose platoon allegedly killed 200 innocents. He was found guilty of personally murdering 22 civilians and sentenced to life imprisonment, but his sentence was reduced to 20 years by the Court of Military Appeals and further reduced later to 10 years by the Secretary of the Army. Proclaimed by much of the public as a “scapegoat,” Calley was paroled by President Richard Nixon in 1974 after having served about a third of his 10-year sentence.
I think some Americans were upset by thinking William Calley deserve to be sent to prison, but not only him.