Kevin Weeks (at right, holding gun) appeared in court Tuesday as a witness in the trial of Whitey Bulger, seated.
The trial of James "Whitey" Bulger descended into an expletive-laced shouting match Tuesday between the alleged mob boss and the former right-hand man who called him a rat.
The outburst happened as Kevin Weeks, who prosecutors say was an enforcer for Bulger's team, was on the stand for a second day, giving graphic testimony about murders that Bulger is accused of committing.
"We killed people who are rats, and the two biggest rats were sitting right next to me," he said, referring to Bulger and a cohort, Stephen "The Rifleman" Flemmi, and their work as FBI informants.
At that point, Bulger, who has been stoic for most of the trial, hissed: "F--- you!"
Weeks yelled back: "F--- you! What are you going to do!"
The judge stepped in to stop the exchange - chiding Bulger - according to an account from a reporter for NBC affiliate WHDH in Boston and New England Cable News.
Carney - you won? Weeks. We killed people who are rats and the two biggest rats were sitting right next to me"— Jonathan Hall (@JHall7news) July 9, 2013
Bulger swears at weeks. Weeks yells "expletive you" in the courtroom. "What are you going to do?" Judge steps in. That was unbelievable.— Jonathan Hall (@JHall7news) July 9, 2013
Earlier Tuesday, Weeks testified that Bulger shot one man, a jewelry thief, in the back of the head after a day of torture, including handcuffing and hog-tying.
Bulger, 83, is charged with killing 19 people as the leader of the Winter Hill Gang in Boston. He has pleaded not guilty to racketeering, extortion and other charges.
U.S. Attorney's Office via AP
James "Whitey" Bulger, left, stands with his former right hand man, Kevin Weeks, in this undated surveillance photo.
He fled Boston in 1994 and was on the run as one of America’s most wanted fugitives for 16 years before his capture in Santa Monica, Calif., in 2011.
Bulger was warned earlier in the trial after prosecutors said they heard him swear at another witness.
Weeks, 57, is key to the prosecution's case and has led investigators to the burial sites of many alleged victims of Bulger’s team. Weeks served five years in prison for five murders and was released in exchange for testifying against Bulger.
In earlier testimony Tuesday, he discussed Bulger’s hatred for informants and said, “We killed informants.”
The trial was in its 17th day Tuesday and could last three months.
The Associated Press contributed to this report.