Ronald Lee Ridenhour was an American whistleblower and investigative journalist known for having played a central role in spurring the federal investigation of the 1968 My Lai massacre in Vietnam. When he first learned of events there, he was serving in the United States 11th Infantry Brigade in Vietnam. He gathered evidence and interviewed people before the end of his tour. After returning to the US in 1969, he wrote to President Nixon, members of his cabinet and two dozen members of Congress recounting what he had learned. A full-scale Department of Defense investigation eventually took place.