A volunteer paramedic on Bloody Sunday says a soldier fired into an Army vehicle where three of the victims lay dead or dying.
Alice Doherty claims the shooting happened after she heard moans from inside the Saracen and saw one of the bodies move.
She told the Saville Inquiry that she'd kept quiet about the incident for fear of further distressing relatives.
She told the hearing in Derry's Guildhall that she saw the shooting along with two other now-deceased civilians.
Mrs Doherty said one of her fellow witnesses, her leader in the paramedic Knights of Malta, Leo Day, had convinced her to keep quiet.
Her account was challenged by Peter Clarke QC, acting for most of the soldiers, who said no one else had seen it happen.
He added: "What I have to suggest is, it is very unfair not just on the soldiers but on the families when you start accusing soldiers of firing into Saracens when they never did it?"
But she insisted: "They did, they did."
Thirteen men and youths were shot dead in the city's Bogside district on January 30, 1972, when paratroopers opened fire in the aftermath of a big civil rights march.
Mrs Doherty said of her decision to recount the alleged episode only now: "I just brought it out because I thought it was time, that the families should know the truth of some of the things covered up on that day. I know it is going to be hard on them."