A policeman sprayed gunfire at wounded, unarmed people and repeatedly stamped on a dying man on a bridge in New Orleans in the aftermath of Hurricane Katrina in 2005, a court heard.
Michael Hunter, a former officer, told the court in New Orleans that he was shocked when Sgt Kenneth Bowen leaned over a concrete barrier and fired an assault rifle at several people who had been shot by police on Danziger Bridge, less than a week after the hurricane struck.
Hunter, who has pleaded guilty to participating in a cover-up to make the shootings appear justified, is a key government witness in the trial of five police officers.
His testimony is the most detailed account of the shootings in the trial so far. It may help explain why police allegedly fired on unarmed residents when they responded to a distress call that other officers were under fire.