A Jewish diamond dealer begged a New York City judge last week to let him remain in prison rather than face retribution for testifying against a mafioso.

Brian Greenwald, former president of Doppelt & Greenwald in Manhattan's Diamond District, made the plea at his sentencing at Manhattan Federal Court last week.

Appearing before Judge Harold Baer, Greenwald, 40, made it clear that he had no wish to leave the cells where he had been sheltered from the mob for 27 months, according to a story in the New York Post.

"I testified against a certain individual who is life-threatening for me," Greenwald told Mr Baer. "I've had to watch my back for organised-crime retaliation. I've learned recently that they are trying to find out where I am," he said.

Greenwald was arrested in 2008 for arranging a bungled hijacking of a FedEx truck containing $1 million in gems. Federal prosecutors also state in court papers that they believe he masterminded a staged robbery of his business in 2005, where thieves tied up employees and grabbed nearly $5 million in gems.

The supposed heist was an insurance fraud, prosecutors say.

As part of his plea deal, he admitted to being a money-launderer for Joe "The German" Watts, a henchman of the late John Gotti, an infamous New York City crime boss.

Watts pleaded guilty in January to setting up the murder of Fred Weiss, a sanitation executive from Staten Island. He is in prison awaiting sentencing, but Greenwald made it clear he still lives in fear.

"I pass sentence - I don't make a decision as to your welfare or survival," said Mr Baer, telling Greenwald that his options were to leave prison now or to wait there for another 60 days while the federal government tried to get him onto the witness-protection programme. Greenwald quickly chose to stay behind bars.