Frank Calabrese Sr., 75, a Chicago hit man who strangled victims and then slashed their throats to be sure they were dead, died Tuesday in a federal prison in North Carolina, authorities said.

Ed Ross, a spokesman for the Federal Bureau of Prisons, had no information on the cause of death, though Calabrese claimed at his sentencing in 2009 that he suffered from a host of ailments, including an enlarged heart.

"It's very emotional right now because there were two sides to my dad, and I miss the good side," Calabrese's son Frank Calabrese Jr. told the Chicago Sun-Times. He had helped put his father behind bars by secretly recording him boasting about mob killings.

Calabrese was among five men convicted in September 2007 at the Family Secrets trial, which resulted from a major, multiyear effort by the federal government to weaken the Chicago Outfit, as the city's organized-crime family calls itself.

The investigation also was aimed at clearing 18 unsolved mob murders dating back to the early 1970s. Calabrese was blamed for many of them and sentenced to life in prison.

It was Chicago's biggest underworld trial in decades and it produced sensational testimony, including a description from his brother of how Calabrese preferred to strangle victims with a rope and then slash their throats to make sure they were dead.

Calabrese laughed during some of the trial's most grisly testimony.

- AP