"Whitey" Bulger Trial: Reputed mob boss killed people for being "rats," but he was one, witnesses say in week 5

(CBS/AP) BOSTON - This week's testimony in the racketeering trial of James "Whitey" Bulger was full of contradictions as it was further instated that Bulger allegedly killed people for being FBI informants, when he was, in fact, an FBI informant himself, according to his once-loyal partner in crime, Stephen "The Rifleman" Flemmi.

PICTURES: Guns and Money: Whitey Bulger evidencePICTURES: James "Whitey" Bulger through the years

Court proceedings were kicked off this week with retired FBI agent Gerald Montanari testifying that Edward "Brian" Halloran, a man allegedly killed by Bulger, predicted his fate. Montanari said Halloran predicted he would be killed if Bulger learned he'd become an FBI informant.

"He said that if Bulger or Flemmi had any indication that he was cooperating with the FBI that they would go to any extreme, even if it meant killing innocent bystanders, including his family," Montanari testified Monday.

Bulger is charged with opening fire on a car Halloran was in May 1982, a few months after he turned informant.

Ironically, prosecutors say Bulger learned of Halloran's cooperation through former FBI agent John Connolly, who was Bulger's handler while he was an FBI informant.

Bulger has vehemently denied assertions that he was a longtime FBI informant who ratted on the rival New England Mafia and other criminals. According to testimony, he told people that being a "rat" was the worst thing anyone could do. His lawyers insist he only paid FBI agents to tip him off to investigations and upcoming indictments.

Midweek, on Wednesday, former U.S. customs agent Donald DeFago testified a man Bulger is accused of killing was cooperating with law enforcement just before he disappeared in 1984.

Bulger is charged with fatally shooting John McIntyre, a fisherman from Quincy, after learning he was talking to authorities. Bulger associate Kevin Weeks testified earlier in the trial that Bulger interrogated and killed McIntyre while he was chained to a chair.

But the trial came full circle by the end of the week when arguably the most anticipated witness was called to the stand. Bulger and his once-loyal comrade Stephen "The Rifleman" Flemmi came face to face Thursday for the first time in nearly two decades as Flemmi testified against the reputed crime boss.

Although he was only on the stand for 15 minutes Thursday, Flemmi's testimony got off to a rocky start when both he and Bulger exchanged obscenities before he took the stand. Afterwards, he began by telling how he and Bulger were secret FBI informants for 15 years while they ran the Winter Hill Gang.

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

Connolly was convicted of tipping off both men in late 1994 that they were about to be indicted. Bulger fled Boston and was one of the nation's most wanted fugitives until he was captured in Santa Monica, Calif., in 2011. Flemmi stayed, was arrested and later pleaded guilty to 10 killings. He is now serving a life sentence.

When Flemmi's testimony continued on Friday, he went on to detail a grisly string of nine killings he says Bulger ordered, approved or carried out with his own hands, including the strangling of the witness' own girlfriend.

Bulger looked straight ahead and took notes on a legal pad during his former partner's testimony. He didn't appear to look at him.

Flemmi testified he set his girlfriend's killing in motion when he blurted out to her something he shouldn't have: that he and Bulger were FBI informants.

Bulger decided Debra Davis knew too much and strangled her in front of Flemmi, the once-loyal associate said in court Friday.

Although Flemmi said he initially refused to go along with Bulger's plan to kill Davis, he admitted he ultimately did nothing to stop it. He is scheduled to return to the witness stand on Monday.

Although things were tense in court this week, the drama wasn't contained to the courthouse. On Wednesday, a former Boston liquor store owner who claimed to have been extorted by Bulger and had hoped to testify against him was found dead. Authorities said a jogger discovered the body of 59-year-old Stephen "Stippo" Rakes in the woods along a street in Lincoln, Mass. A cause of death has not been determined but police have called the death "suspicious," according to CBS Boston.

Friends said Rakes was eager to testify against Bulger. 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.

Bulger, now 83, is accused in a 32-count racketeering indictment of playing a role in 19 killings in the 1970s and '80s while he allegedly led the Winter Hill Gang. He is also charged with money laundering and extortion.

Assistant U.S. Attorney Brian Kelly told Judge Denise Casper that prosecutors expect to wrap up their case next week. Bulger's lawyer, J.W. Carney Jr., said the defense case could go through August.

Testimony began June 12.

Complete coverage of the Whitey Bulger case on Crimesider