Notorious Boston mobster James “Whitey” Bulger has asked the U.S. Supreme to appeal his case, NBC News reported. He is currently serving two life sentences for his 2013 conviction on racketeering charges and his connection to 11 murders during the 1970s and '80s.

The premise to his appeal, according to Bulger’s lawyer Hank Brennan, is that Bulger did not get a fair trail due to details of an immunity deal promised to the ex-gangster by a now deceased prosecutor being withheld from jury members. At the time, a three-judge-panel ruled he didn’t have sufficient evidence proving that such agreement existed.

Bulger, 86, filed an appeal for a new trial that was denied just a few months ago in March. Brennan noted in a recent interview with Boston public radio station WBUR that his client’s latest appeal didn’t look all that promising, either. However, Bulger is still fighting for his freedom.

"There's very little hope," Brennan said. "It's like catching lightning in a bottle. But the idea that someone has the right to defend himself in this country no matter who they are, even James Bulger, is of such importance that I don't think I could pass on the idea."

According to Brennan, Bulger’s denied appeal violated his right to present a defense and restricted him from testify on his own behalf, which Brennan says is an “error” that “affected the fundamental fairness” of the trial, CBS News reported. In the appeal, which was filed Aug. 11, Brennan also claimed federal prosecutors withheld information regarding “promises, rewards and inducements” made to John Martorano, who testified against Bulger during his 2013 trial.

Martorano was a hit man that worked for Bulger while he operated a dangerously violent Boston gang from the 1970s throughout the early 1990s. Bulger fled Boston in 1994 in attempt to prevent being captured by the fed. However, he was finally captured in Santa Monica in 2011.

Bulger’s appeal must be responded to by federal prosecutors by Sept. 12.