During the last four decades the My Lai Massacre has been dealing with in many studies on the history of the so-called "The Vietnam War". However, most of studies on My Lai were focused on the description of the event and the stories concerning the Court-Matial against some officers and soldiers who committed in this famous war crime. In this article, the author provides firstly a brief description of the massacre. He then analyzes the process through which the massacre was uncovered and brought to the court-matial. Finally, the author analyzes and points out the origins of the war crimes committed by the US Army during the Vietnam War.