It is the duty of every American soldier to ensure that [the Geneva Conventions] are upheld, and the responsibility of violations rests in a certain measure upon those who do not report violations they have witnessed. You imply that this goes on at other than the individual level; yet, there is always a higher headquarters to which violations can be referred and channels exist to which these reports can be made. You ask: "Does his presence in a combat zone and his possession of a rifle absolve a soldier from moral responsibility?" The answer to that is, of course, No. But neither is a person who keeps silent when he witnesses a war crimes absolved of responsibility for that crime because he did not actively participate in it.*This is certainly the correct legal, moral, and ethical response, but when considered in relation to My Lai, seems a bit naive. Hugh Thompson and Chaplain CPT Creswell both reported the massacre to higher authority, and radio intercepts of the conversations among the helicopter pilots were made, but the officers of Task Force Barker were successful in their cover-up of what happened at My Lai. Only letters to Congress and media coverage brought any action. The dozens of other men who witnessed the massacre, including those who refused to take part, did nothing to report the massacre to the authorities, and themselves took part in hushing things up when COL Oran K. Henderson and LTC Frank Barker conducted their sham of an investigation of their own units. What I'm trying to get at is how those guys rationalized their noninvolvement and lack of intervention when they witnessed what were clearly war crimes.
Michael Bilton and Kevin Sim, Four Hours in My Lai. New York: Viking, 1992.