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

Calabrese, 75, died Tuesday at the Butner Federal Medical Center, said Ed Ross, a spokesman for the Federal Bureau of Prisons. Ross 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.