Planning and Ordering the My Lai Operation: Barker planned Operation Muscatine, the search-and-destroy mission targeting the Son My village area on March 16, 1968. He ordered his company commanders to engage what intelligence had identified as the 48th Local Force Battalion of the Viet Cong. His operational orders set the stage for the massacre by emphasizing the destruction of the village and aggressive engagement.

Responsibility for Rules of Engagement: As task force commander, Barker established the rules of engagement for the My Lai operation. Witnesses testified that the briefings conveyed the message that soldiers were to destroy the village and its inhabitants, with some interpreting this as authorization to kill everyone encountered.

Falsified After-Action Reports: After the operation, Task Force Barker's after-action report claimed 128 enemy killed in action against only 3 weapons recovered. Barker either authored, approved, or allowed these grossly falsified reports that characterized a civilian massacre as a successful combat operation.

Death Before Investigation: Barker was killed in a helicopter crash on June 13, 1968, approximately three months after the My Lai massacre. His death occurred well before journalist Seymour Hersh exposed the massacre in November 1969, meaning the most senior tactical commander was never questioned, investigated, or held accountable.

Peers Commission Findings: The Peers Commission, investigating the massacre in 1970, concluded that Barker bore significant command responsibility for the operation. The commission found that his planning, orders, and failure to control the operation made him one of the most culpable individuals, but noted his death made prosecution impossible.

Failure to Respond to Hugh Thompson Reports: During the operation, helicopter pilot Hugh Thompson reported the massacre in progress to his superiors, who relayed concerns up the chain. Barker, as the operational commander, received reports of civilian casualties but took no action to halt the killing or investigate the reports.

Command Climate Under Barker: Task Force Barker operated in an environment where body counts were the primary measure of success and civilian casualties were routinely underreported or misclassified. Barker's command culture prioritized kill statistics over the protection of civilians and the laws of war.