"In the first, he was assigned to investigate the 1968 U.S. massacre at My Lai and found no wrongdoing."
https://www.bbc.com/news/world-us-canada-33957894
"He was assigned to investigate a letter from a serving soldier that reinforced allegations of a massacre at My Lai in March 1968, in which US soldiers killed hundreds of civilians, including children.
Powell's conclusion, that "in direct refutation of this portrayal, relations between American soldiers and the Vietnamese people are excellent", flew in the face of growing evidence of brutal treatment of civilians by US forces.
He was later accused of "whitewashing" the news of the massacre, details of which did not finally become public until 1970."
rifled through some quick links in google, and it looks even the mainstream retrospectives mention it.
https://www.bloomberg.com/news/articles/2021-10-18/colin-powell-u-s-army-general-turned-top-diplomat-dies-at-84
"In the first, he was assigned to investigate the 1968 U.S. massacre at My Lai and found no wrongdoing."
https://www.bbc.com/news/world-us-canada-33957894
"He was assigned to investigate a letter from a serving soldier that reinforced allegations of a massacre at My Lai in March 1968, in which US soldiers killed hundreds of civilians, including children.
Powell's conclusion, that "in direct refutation of this portrayal, relations between American soldiers and the Vietnamese people are excellent", flew in the face of growing evidence of brutal treatment of civilians by US forces.
He was later accused of "whitewashing" the news of the massacre, details of which did not finally become public until 1970."
Perfect, time to go piss off my friends!