On 16 March 1968, Henderson took over as commander for the 11th Infantry Brigade. He would oversee a battalion-sized operation to clear
Viet Cong forces from the
Sơn Tịnh District, ordering his men to "go in there aggressively, close with the enemy and wipe them out for good". During the operation, soldiers under his command massacred hundreds of unarmed South Vietnamese civilians near the village of Sơn Mỹ in what would later be known as the
My Lai massacre. At the time of the massacre, Henderson was flying over the villages in a helicopter. Henderson was the first to interview
Warrant Officer (WO1)
Hugh Thompson, Jr., a helicopter pilot who had intervened in the massacre and issued an official report describing what he saw. Despite the report, Henderson issued a commendation for Captain
Ernest Medina, the commander of one of the companies involved in the killings and even after interviewing several soldiers involved in the operation, issued a report stating only twenty civilians had been inadvertently killed by artillery fire. In his report, Henderson called widespread reports that hundreds of civilians had been killed "propaganda" to discredit U.S. and ARVN forces. In 1970, three charges were brought against Henderson including failing to carry out a thorough investigation of the killings, failing to report possible atrocities to his division commander Brigadier General
Samuel W. Koster, and lying to a Pentagon inquiry. In the case, Henderson's defense counsel argued that he had conducted an honest investigation but was misled by his subordinates including Captain Medina while prosecutors contended he hid evidence in order to preserve his rank and command. On 18 December 1971, after a 62-day trial in
Fort George G. Meade which heard 106 witnesses, Henderson was acquitted by a jury of two generals and five colonels. After his acquittal, he stated that the verdict "reaffirms the confidence any Army man can have in the military system." ==Later life==