A Jewish diamond dealer has begged a New York City judge to let him remain in prison rather than face retribution for testifying against a member of the Mafia.

Brian Greenwald, 40, former president of Doppelt & Greenwald in Manhattan's diamond district, made the plea at his sentencing at Manhattan Federal Court. Appearing before Judge Harold Baer, Greenwald said: "I testified against a certain individual who is life-threatening for me. I've had to watch my back for organised-crime retaliation".

Greenwald was arrested in 2008 for arranging a bungled hijacking of a FedEx truck containing $1 million in gems. As part of his plea deal, he admitted to being a money-launderer for Joe "The German" Watts, a notorious henchman for the late John Gotti, an infamous New York City crime boss.

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

But the judge told Greenwald that he could leave prison immediately or stay there for a further 60 days while the government tried to get him into the witness-protection programme. Greenwald chose to stay behind bars.