CHICAGO (CBS) — An elderly mob thief has been convicted of racketeering charges for plotting a series of robberies with two other geriatric mobsters, who had already pleaded guilty to helping plan the heists.

Arthur “The Genius” Rachel, 73, opted for a bench trial last week after co-defendants Joseph Jerry “The Monk” Scalise and Robert “Bobby” Pullia pleaded guilty in the case.

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On Thursday, U.S. District Judge Harry Leinenweber found Rachel guilty on three of the four charges he faced for plotting the robbery of an armored car at a bank in LaGrange and a break-in at the Bridgeport home of the late Outfit boss Angelo “The Hook” LaPietra.

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Rachel could face a life sentence for his convictions.

Assistant U.S. Atty. Amarjeet Bhachu said, “You don’t get a ‘Get Out Of Jail Free’ card because you commit a crime when you’re a senior citizen.”

Rachel, Scalise and Pullia were arrested outside the LaPietra home in 2010 before they managed to pull off any of their plans.

Rachel and Scalise have been in prison before, serving 13 years in a British prison after stealing the 45-carat Marlborough diamond from a London jewelry store in 1980.

After pleading guilty last week, Scalise said off-camera that he might spill the beans on what happened to the diamond, which was never recovered after the robbery. Law enforcement officials have said they believe the thieves broke up the diamond into smaller gems and resold them.

Prosecutors have said the aging trio planned a number of scores: a holdup of a Davis Bancorp armored truck outside the First National Bank of La Grange, breaking into the home of the late mob boss Angelo “The Hook” La Pietra and robbing the State Bank of Countryside.

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FBI agents said they were planning to use heavy weapons in at least one of the planned heists.

FBI tape recordings released revealed the plotters, who were allegedly armed with automatic weapons, planned a hot time for the armored truck guards if they resisted.

“If he tries to get out, spray him,” Scalise tells Arthur “The Brain” Rachel in one recorded conversation.

“The biggest, the biggest gun we got. I wanna be with the biggest ****ing gun,” Rachel said.

“If he tries to get out, just spray that door. Just spray ‘em to keep him in,” Scalise said.

The FBI tapes also revealed, while conducting surveillance at LaPietra’s home, Scalise and his cohorts laughed at how cranky LaPietra had become while spending his sunset years at his Italian social club.

“He was a miserable person. When he got out of jail he used to sit in the club, in the corner, in a chair, and just stare at everybody. Nobody wanted to go there,” Scalise said.

Although Scalise and Pullia had pleaded guilty, their attorneys made it clear they were not cooperating with the feds.

When asked outside of court if the Marlborough Diamond might ever be found, Scalise said last week, “If Lloyd’s [of London] wanted to pay enough money, they could.”

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Leinenweber acquitted Rachel of a count of being a felon in possession of a firearm, saying prosecutors didn’t prove he ever had a gun in his possession.