BOSTON (AP) — His hands on his hips in a you-want-a-piece-of-me stance, Stephen "The Rifleman" Flemmi glared at James "Whitey" Bulger in the courtroom, and the two men snarled what sounded like obscenities at each other.

Bulger and his once-loyal comrade came face to face Thursday for the first time in nearly two decades as Flemmi testified against the reputed Boston crime boss at Bulger's racketeering trial.

In his brief 15 minutes or so on the stand before court recessed for the day, Flemmi, a ruthless underworld executioner, told how he and Bulger were secret FBI informants for 15 years while they ran the Winter Hill Gang, the city's murderous Irish mob.

Flemmi said he was with Bulger and heard him give information to FBI agent John Connolly "hundreds of times" over 15 years.

That comment seemed to rankle Bulger, who insists that he was never an informant and told people that being a "rat" was the worst thing anyone could do, according to testimony.

Flemmi is scheduled to return to the stand on Friday for what could be a combustible session. Both men are renowned for hair-trigger tempers. And one thing that has really set Bulger off in court is being called a rat.

Before Flemmi took the stand, word spread through the courtroom that a former Boston liquor store owner who had hoped to testify against Bulger and openly despised him had been found dead. Authorities said a jogger discovered the body of 59-year-old Stephen "Stippo" Rakes on Wednesday in Lincoln, Mass.

The medical examiner's office said an autopsy Thursday found no signs of trauma. Investigators were awaiting the results of toxicology tests.

In court, Bulger shot Flemmi a look just after he described the extent of Bulger's informant activities.

Then, as testimony ended for the day and the jury was led out of the courtroom, the 79-year-old Flemmi stood up so that federal marshals could take him away. As he stood there, he put his hands on his hips and glowered at the 83-year-old Bulger, who was about 10 feet away at the defense table.

The two men exchanged obscenities, but people in the courtroom who heard the words differed on exactly what was said. No transcript was made available.

Flemmi testified that he and Bulger provided information mostly on the rival Italian mob, but also on "different people from South Boston."

"Who did most of the talking at these meetings?" prosecutor Fred Wyshak asked.

"James Bulger," Flemmi replied.

Flemmi was asked to describe his relationship with Bulger.

"Strictly criminal," he replied.

But he also said they were close friends, socialized together and went to Europe together.

Asked to describe Bulger's personality, Flemmi replied, "Overbearing," then added, "Forceful."

Prosecutors said Bulger and Flemmi ran the Winter Hill Gang for more than 20 years, making millions by extorting drug dealers, bookmakers and loan sharks.

Bulger is accused of participating in 19 killings during the 1970s and `80s. Flemmi pleaded guilty to 10 killings, extortion, drug distribution and other charges. He is serving a life sentence.

Flemmi said he hasn't seen Bulger since about a week before Christmas in 1994. That was when they got tipped off by Connolly, their former FBI handler, that they were about to be indicted.

Bulger fled Boston and was one of the nation's most-wanted fugitives for more than 16 years until he was captured in Santa Monica, Calif., in 2011.

Flemmi was arrested and has been in prison ever since.

Bulger has already had two profanity-laced outbursts during the trial, one directed at his former protege, Kevin Weeks, and the other at a former FBI agent who admitted taking payoffs from Bulger.

As for the dead witness, prosecutors said Rakes and his former wife were forced to sell Bulger their store in 1984 to use as a headquarters for his gang and as a source of legitimate income.

But Weeks, Bulger's former right-hand man, gave a differing account when he testified last week. Weeks said Rakes wanted to sell the store, agreed to a price and then tried to increase the price.

Friends said Rakes was eager to testify against Bulger.

"The day I see him in a box, not breathing, will be better," Rakes told The Associated Press in April.

But when prosecutors listed their remaining witnesses for the judge Tuesday, Rakes wasn't among them. Rakes was upset when he left the courthouse Tuesday, said Steven Davis, the brother of one of Bulger's alleged victims. Davis said he wasn't sure why.

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