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".

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.

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.

"[10] After leaving the Army in 1974, Henderson became head of the Pennsylvania Emergency Management Agency, where he oversaw responses to devastating floods in 1977 and the Three Mile Island accident.