"The defendant has committed one heinous crime after another," said Assistant U.S. Attorney Brian Kelly. "The carnage that he has caused is grotesque."
Bulger, now 84, was convicted in August in a broad indictment that included racketeering charges in a string of murders in the 1970s and '80s, as well as extortion, money-laundering and weapons charges.
At least a dozen family members of people Bulger was convicted of killing were expected to speak at the two-day hearing. The first to do so was Sean McGonagle, the son of Bulger victim Paul McGonagle. He called Bulger "Satan," a "domestic terrorist" and a "sad, lonely and irrelevant old man."
Bulger, wearing an orange prison jumpsuit, stared down at the defense table and did not look at victims' relatives as they spoke.
His attorneys said he refused to provide any information to probation officials preparing a report for Judge Denise Casper, who will sentence him. Attorney J.W. Carney Jr. said he would make no sentencing recommendation because his client believed his trial was a sham.
Bulger also called his trial a sham in August after he was not allowed to use as a defense his claim that a now-deceased federal prosecutor gave him immunity to commit crimes. He did not testify.
He can speak at the sentencing hearing if he wants, but it's not known if he will.
The federal jury that convicted Bulger found prosecutors proved he played a role in 11 of 19 murders.
Jurors found the government had not proven Bulger participated in seven other killings and were unable to reach a verdict in another. But Casper ruled Wednesday that relatives of all 19 people can speak at the sentencing too, despite objections from Bulger's attorneys.
Bulger, the former head of the Winter Hill Gang, fled Boston in 1994 ahead of an indictment and spent more than 16 years as a fugitive before being captured in Santa Monica, Calif., in 2011.