The original official report which appeared on the front page of the New York Times said it was a combat engagement that left 120 Vietcong dead.
In reality over 500 civilians, mostly women and children, were killed in cold blood.
18 months later Seymour Hersh received an anonymous tip and the public finally learned the truth.
The mainstream news media had zero interest in his research. Only a small, independent publication was willing to cover the story.
A little know part of the story is that it was an America helicopter commander who after stumbling on the massacre stopped it by ordering his men to train their weapons on the troops who were committing the atrocities.