Despite Connolly's conviction and Flemmi's testimony, Bulger's lawyers have argued in this trial that he was not an FBI informant.
Authorities say Connolly, who was raised in the same housing projects as Bulger, cut a deal with the alleged mob figure in 1975. Bulger would give information about the Italian mob -- the FBI's prime target -- while Bulger, authorities said, got names of rival gang members and other informants who had dirt on him. He is accused of killing those people.
Without that FBI protection, prosecutors say, Bulger and Flemmi's reign of terror would not have been as successful or lasted as long as it did, from the early 1970s through the mid-1990s.
Bulger rose to the top of the notorious Winter Hill gang, prosecutors say, before he went into hiding for more than 16 years after the crooked FBI agent told him in December 1994 he was about to be indicted on federal racketeering charges.
He was captured in Santa Monica, California, two years ago, living under a false name with his girlfriend in an apartment in the oceanside city. The girlfriend, Catherine Greig, was sentenced to eight years in prison last summer for helping him evade capture.
At his arraignment in July 2011 he pleaded not guilty to the 19 murder charges and 13 other counts.
Through his lawyers, the 83-year-old defendant had argued he was given immunity by the FBI and a former prosecutor. The judge dismissed the claim, saying any purported immunity was not a defense against crimes Bulger faces.
Prosecutors plan to call two more witness Friday, and expect to rest their case on the 30th day of trial.
The defenses amended witness list, which was cut virtually in half to 32 witnesses last week, was whittled down to a potential 16 witnesses after Judge Denise Casper ruled some witnesses irrelevant and the defense withdrew a handful. The list is subject to further change.
Among those virtually certain to testify are four FBI agents who the defense says will testify Bulger was not an informant for FBI in Boston.
The government argued that Bulger is not "charged" with being an informant and the testimony could confuse jurors. But Casper said that, "given the centrality of the government's allegation of Bulger being an informant to all of the matters in this case, I think those are proper witnesses."
Also on the stand Thursday afternoon was bar owner Kevin O'Neil, one of the O's in "Triple O's Bar," an establishment that doubled as one of Bulger's many headquarters in the 1970s and '80s. O'Neil said he had Bulger on the payroll, but he was never an employee.
When prosecuting attorney Zachary Hafer asked why he was on the payroll, O'Neil responded, "He asked."
Hafer: "Why didn't you say 'No'"?
O'Neil: "I didn't think it was smart."
O'Neil testified that in Christmas of 1994 he got a call from Connolly, who said, "Get ahold of the kid because his friend has a problem."
In rapid-fire questioning, Hafer asked, The Kid?--"Kevin Weeks"; the friend?--"Jim Bulger"; the problem? --"I believe indictments."
O'Neil testified that he then saw Connolly talking to Weeks shortly after that call.
O'Neil said he never saw Bulger again after that day.
Prosecutors say Connolly tipped Bulger off to a 1995 indictment, causing Bulger to go on the run, landing himself on the FBI's top 10 most wanted list before being arrested in California.