At base headquarters, Thompson filed charges of mass killings, causing the command to order a cease-fire a little before noon that doubtless saved hundreds more lives.
Thompson’s allegations greatly unsettled the commander of Americal, Major General Samuel Koster, who was on the fast track to promotion and was already worried about a report that American forces had killed 128 Viet Cong but discovered only three weapons. The immediate question was whether the victims were unarmed.
Koster’s second in command, Brigadier General George Young, expressed doubt that Thompson witnessed mass killings and was more disturbed about his “so-called confrontation” with fellow American soldiers.
Rather than file an atrocity report, Koster decided to keep the matter within the division by ordering an informal investigation aimed at collecting facts and then reporting back to him. He saw no need for an official inquiry, which would involve appointing an investigating officer, taking sworn testimony of witnesses, and submitting a final report to the Staff Judge Advocate of MACV (Military Assistance Command, Vietnam). As Young later emphasized to the Army’s Criminal Investigation Division, “One must be aware that a war crime has been committed before it can be reported.”
That statement was not correct. MACV Directive 20-4 required reports on “all alleged or apparent war crimes” inflicted by “US military personnel upon hostile military or civilian personnel.” Mere suspicion of a war crime required a formal investigation.
On March 18, five officers gathered in the command post van of the architect of the assault, Lieutenant Colonel Frank Barker, to discuss Thompson’s charges. “Nobody knows about this except the five people in this room,” Young declared to Barker, Colonel Oran Henderson (Americal’s brigade commander), Lieutenant Colonel John Holladay (battalion officer at Chu Lai), and Major Frederic Watke (Thompson’s aviation commander).
In accordance with Koster’s order, Young instructed Henderson to interview personnel who had been on the ground or in the air at My Lai and present an oral report to Koster within seventy-two hours.
Later that same morning, Henderson met with Thompson for about a half hour in Barker’s van. He also met with Colburn and a Huey gunship pilot, Warrant Officer Jerry Culverhouse, who both later testified that they confirmed Thompson’s charge of indiscriminate killing. Yet Henderson later claimed that he talked only with Thompson, who, he said, mentioned nothing about mass killings or of rescuing a small group of civilians from American soldiers. On March 20 Henderson presented his oral report: no evidence of war crimes. All soldiers interviewed denied knowledge of any atrocities.
Shortly afterward, the Americal Division awarded medals for heroism to Thompson, Andreotta, and Colburn for risking their lives in a crossfire between U.S. and Viet Cong forces to save sixteen Vietnamese children.
The Americal Division had fabricated an account of bravery aimed at silencing them. Two years later, a congressional subcommittee used the awards in an attempt to undermine the credibility of Thompson and Colburn by showing that they (along with Andreotta, who had died in battle a month after the massacre) had received medals for bravery in combat when no enemy was present.