Direct Knowledge of the Massacre: Henderson received urgent reports from helicopter pilot Hugh Thompson on the day of the massacre, indicating that American soldiers were killing unarmed civilians. Henderson personally flew over My Lai in a command helicopter and would have seen evidence of the killing. Despite this direct knowledge, he took no action to halt the operation or rescue civilians.

Fraudulent Investigation and Cover-Up: After receiving Thompson's reports, Henderson conducted a sham investigation that concluded no massacre had occurred and that civilian casualties were the result of normal combat operations. This fraudulent investigation became the foundation of the official cover-up that concealed the massacre for over 18 months.

Highest-Ranking Officer Tried: Henderson was charged with dereliction of duty and cover-up and became the highest-ranking officer to face trial in connection with My Lai. The Peers Commission had recommended charges against more senior officers including Major General Samuel Koster, but Henderson bore the burden of representing command accountability at trial.

Acquittal by Military Jury: Henderson was acquitted by a military jury in December 1971. His defense argued that he had reasonably relied on the reports of subordinates and that the fog of war prevented him from fully understanding what had occurred. The jury's acceptance of this defense effectively established that no commander bore responsibility for the massacre.

Suppression of Thompson's Reports: When Hugh Thompson reported the massacre through his chain of command, Henderson was positioned to receive and act on those reports. Instead of ordering a cease-fire and investigation, Henderson allowed the official after-action report to characterize the operation as a successful engagement against 128 enemy fighters, despite knowing this was false.

Command Responsibility Failure: Henderson had both the authority and the responsibility to prevent, halt, and investigate the massacre. As the brigade commander, he had the power to order a cease-fire, deploy forces to protect civilians, and launch an immediate investigation. His failure to exercise any of these powers constituted a catastrophic failure of command responsibility.

Peers Commission Findings: The Peers Commission found that Henderson bore significant responsibility for both the failure to prevent the massacre and the active cover-up afterward. The commission documented how Henderson's cursory investigation was designed to reach a predetermined conclusion that no wrongdoing had occurred.