Editor's note: This article contains language some readers may find offensive.
(CNN) -- Two days of testimony by a former partner of reputed mob boss James "Whitey" Bulger ended dramatically Tuesday when Kevin Weeks and Bulger -- once so close that they spoke nearly every day for more than a decade -- shouted at one another across a federal courtroom in Boston.
Bulger's lawyer, J.W. Carney, tried to portray Weeks as an opportunist who knew how to manipulate the system, someone who cut a deal with prosecutors to serve just five years in prison for aiding and abetting five killings, several of which, Weeks testified, he saw Bulger commit.
"You won against the system," said Carney.
"What did I win? What did I win," Weeks said, his voice sounding strained and tired. "Five people are dead."
Asked whether that bothered him, Weeks shot back, "We killed people that were rats, and I had the two biggest rats right next to me ..."
At that, Bulger turned and hissed, "You suck."
"F--- you, OK," snapped Weeks.
"F--- you, too," shouted Bulger as the jury watched.
"What do you want to do?" said Weeks, his eyes locked on Bulger, who was flushed and staring right back.
U.S. marshals stood between the two men, and U.S. District Judge Denise Casper instructed them both to follow the rules of the court before Weeks was dismissed, his testimony over.
Bulger is charged in the deaths of 19 people during some two decades when prosecutors say he ran Boston's Irish mob. He also faces charges of extortion, racketeering and money laundering.
Prosecutors spent most of the morning questioning Weeks about killings he said he saw Bulger commit.
Weeks recounted to the court graphic details of how Bulger killed Arthur "Bucky" Barrett, Joey McIntyre and Deborah Hussey.
In the summer of 1983, Weeks said Bulger organized a meeting with Barrett under the guise of having stolen diamonds that he needed to have taken off his hands.
When Barrett arrived at the house, Bulger, his crime partner Steve Flemmi and Weeks were waiting.
The group then chained Barrett to a chair and grilled him for hours about a rival gang and local drug dealings, Weeks said.
Barrett tried to buy his way out of being killed, describing to Bulger where he had hidden $40,000 in cash.
Weeks said Bulger left the house to pick up the cash while he and another associate watched Barrett.
When Bulger returned to the house, he instructed Barrett to walk down to the basement. Then Bulger put the gun to the back of Barrett's head, pulled the trigger, and according to Weeks, "nothing happened."
When Bulger realized that the gun's safety was still on, he removed it and shot Barrett.
Weeks said he also saw Bulger shoot McIntyre in the same house where he killed Barrett. His methods were the same, too -- he chained McIntyre to a chair, where he admitted to letting authorities capture a boat carrying 40 tons of marijuana slated for sale by Bulger and his gang.
"Jim Bulger took out a rope and started strangling McIntyre; it was too thick, it just gagged him and then Jim asked the victim, 'do you want one to the head?' " Weeks said.
McIntyre said, "Yes sir," and Bulger shot him five times.
Weeks said he also witnessed the killing of Deborah Hussey in that same home.
On a day in early 1985, Weeks said he came downstairs after hearing a "thud" and saw Bulger strangling Hussey, whose lips turned blue as her eyes rolled back into her head.
After each of the three slayings, Flemmi prepared the bodies to be buried by removing the victims' teeth. This practice earned him the nickname "Dr. Mengele," after the infamous Nazi physician, Weeks said.
The victims were buried in the basement of the house only to be moved to another makeshift grave because the owners of the house were selling it.
"It was cheaper to move the bodies than buy house," Weeks explained.
Most of the cross-examination focused on Weeks' decision to testify against his former crime partners, including Bulger, Steven Flemmi and rogue FBI agent John Connolly. Weeks acknowledged that Bulger hated informants, explaining South Boston's code as: "You never give up your friends. You never rat on your enemies. You take care of your own business."
At times Weeks seemed apologetic, saying he had hoped Bulger would never be caught "so he wouldn't be in the circus we're in."
After escaping a 1995 indictment, allegedly on a tip from a rogue FBI agent, Bulger went into hiding for 16 years, landing himself on the FBI's most wanted list before being arrested with his girlfriend in Santa Monica, California, in 2011.
However, Weeks defended his actions, saying he had been shown Bulger's informant file by fellow South Bostonian, or "Southie," and disgraced FBI agent John Connolly and that, "You can't rat on a rat." He says no one has given him any trouble since he returned to South Boston, not even the Italian mafia, which allegedly continues to operate.
When Bulger's lawyer suggested Weeks had lied at times, Weeks shot back almost in disbelief: "I've been lying my whole life. I'm a criminal." But he clarified that his lies were confined to smaller matters, not the testimony he has provided at nearly five trials.
Carney asked, "What lies do you tell your wife?"
"I'm not cheating," said Weeks by way of explanation.
"Does she know you're lying?" asked Carney.
"We're divorced," Weeks responded.