(CNN) -- Reputed mob boss James "Whitey" Bulger slouched uncharacteristically in his chair Monday, muttering "I'm not (a) f***ing informant."
But his 700-page FBI file and informant card show otherwise -- that Bulger provided information on murders, drug deals, armed robberies and criminal fugitives, leading to several arrests.
Bulger ratted on La Cosa Nostra, rival gangs and seemingly anyone -- except those in his small, immediate circle known as the Winter Hill gang.
According to entries in his informant file, Bulger knew he could get away with it and even told his FBI handler he was more likely to be killed by "gangland warfare" than because he was informant since "no one would believe it." Bulger also defended what he called the "professionalism" of the FBI.
Bulger is charged with 19 counts of murder after the FBI found him hiding out in a Santa Monica apartment with his girlfriend in 2011. He was on the lam for 16 years after allegedly being tipped off to a 1995 indictment by his rogue handler, former FBI agent John Connolly, who is now behind bars.
From day one of Bulger's trial, his lawyers have tried to convince the jury that Bulger was not an informant -- something attorney J.W. Carney described as the worst thing an Irishman from South Boston could possibly be.
With the jury out of the courtroom, prosecutor Fred Wyshak mocked the suggestion, saying he would "not engage in the fiction" -- pointing to 15 years of detailed FBI reports.
"Whether it's the ego of the defendant or his reputation he wants to preserve that he was not an informant ... it's a ridiculous contention," said Wyshak, who successfully prosecuted Connolly's case in 2008.
The defense has filed a motion asking to admit into evidence statements made by Wyshak in the 2008 trial claiming that Connolly made false statements in his informant files. The motion has not yet been addressed in court.
James Marra of the Justice Department's Office of the Inspector General testified about numerous file entries saying Connolly, Bulger and Bulger's criminal partner Steven Flemmi "frequently met together as a team."
Documents also expose that Bulger met with more than one FBI agent, including now-disgraced former FBI supervisor John Morris. Morris pleaded guilty to accepting bribes from Bulger in exchange for information. He is cooperating with the government in exchange for immunity and is set to testify against Bulger this week.
Bulger's defense lawyer Hank Brennan said prosecutors "can't have it both ways," since Connolly is a convicted liar who, he said, fabricated Bulger's 8-inch-thick file and his status as an informant.
Judge Denise Casper weighed in, asking, "Why can't both be true?"
The judge said perhaps the definition of "informant" was the issue. Responding to Bulger's claim, Casper said the "veracity of information may be in dispute, (but not) that he was a registered informant."
Along with the 700-page informant file, prosecutors also showed the jury a 3-by-5 card that they called Bulger's "informant card" with his ID number: BS1455 OC. The OC stands for "organized crime."
When Brennan accused the Department of Justice of having a history of "inappropriate relationships with crime figures" even when it came to murder, the judge shut him down.