CHICAGO (CBS) — Threats of violence have canceled scheduled book signings by a mob informant.

Borders bookstores pulled the plug after receiving a threatening voicemail. The book is entitled “Operation Family Secrets,” and it’s by Frank Calabrese Jr. – a man who turned on his notorious father and sent him to prison for life.

“Our Oak Brook store received a voicemail threatening violence. Given the controversial nature of the book we viewed this as a legitimate threat,” a Borders spokeswoman said.

Calabrese told CBS 2’s John Drummond he understands why the chain canceled his Chicago and Oak Brook appearances. He has other local stops along his book tour.

 ”Borders is taking this serious … I can’t blame them,” Calabrese said. “I’m not worried about sales of the books. I don’t want to see nobody get hurt.”

LISTEN: Borders Cancellation Not A PR Stunt, Calabrese Tells Newsradio 780′s John Cody

Calabrese is 50. At one time, he was an aspiring Outfit enforcer being mentored by his father, the mob hitman Frank Calabrese Sr. While both men were imprisoned on juice-loan and gambling convictions, the son became disillusioned and did the unthinkable: He wore a wire against his dad and helped implicate him in seven gangland murders.

“If I would’ve lifted up my shirt, everybody in the yard would have known I had a recorder on,” Calabrese Jr. said. “I wouldn’t have never made it more than 20 feet. I would have been dead.”

Young Calabrese never committed a murder. But at one time he got the contract to murder a fellow mobster. He even practiced for the hit, but his uncle dissuaded him from taking part. 

In explaining his decision to turn against his father and help the feds, Calabrese Jr. said he wanted to change his ways for the better, even though that could have gotten him killed on the outside. The downside of that option was that he would be known as a rat.

“I don’t feel I’m a rat. I don’t,” Calabrese Jr. said. “I didn’t hide behind the scenes and get people in trouble. I stood out there, and I went up against my dad.”

Calabrese testified against his father in the federal government’s “Operation Family Secrets” trial, which concluded with the racketeering convictions of several members of Chicago’s Outfit who were tied to multiple murders.

Despite telling tales out of school, Calabrese has refused to change his identity or go into the witness protection program.

“My life is in a different city now,” he said. “The rest of my family lives here. My brothers live here, my mother lives here. I have cousins that live here, and I just don’t want anybody to do anything to them because they feel that they can’t get me.”

 Asked who is running the Outfit today, Calabrese says: “I don’t have any idea … It’s nice that I don’t have to know anymore.”

Frank Calabrese Sr. is now serving a life sentence in isolation at a federal prison in Springfield, Mo.