An on-and-off-again government motion is dead on trimming the 50-year prison sentence of disbarred ex-law firm chairman Scott Rothstein for engineering a $1.2 billion Ponzi scheme.

U.S. District Judge James Cohn ruled Monday that federal prosecutors “clearly may withdraw” their motion for a reduced sentence tied to Rothstein's commitment to fully cooperate.

Prosecutors didn't offer details for why they scrapped the offer initially made in 2011, and Rothstein argued they lacked that power. Without a hearing, the Fort Lauderdale judge ruled in the government's favor on a question of law.

Rothstein, 55, was leading the 70-attorney Rothstein Rosenfeldt Adler when he pitched investments in fake legal settlements and forged court documents, scamming hundreds of people including auto magnate Ed Morse.

Rothstein later testified his entourage was “living like rock stars.” He plowed investor funds into an opulent office, an extensive watch collection, a Bugatti, a waterfront Fort Lauderdale mansion, a New York condo and other luxuries. A condo unit near the firm's Fort Lauderdale office was used for sex and drug parties.

He hopped a Gulfstream jet to Morocco for eight days when the fraud collapsed in 2009, then returned to face justice. One of the first things he did in custody was inform on mob figures who weren't tied to Florida's biggest fraud.

Under a deal, Rothstein pleaded guilty to three conspiracy and two wire fraud counts. A handful of other attorneys were convicted in the fallout, which extended to illegal campaign contributions.

A year after Rothstein's sentencing, prosecutors filed the motion for a reduced sentence while asking for a stay on the decision “because Rothstein's cooperation was still ongoing,” Cohn wrote. Prosecutors pulled the plug on it last September.

Rothstein has been held by the U.S. Bureau of Prisons in secrecy, making his latest public appearance six years ago for depositions in his defunct law firm's bankruptcy case. His attorney described the 50-year sentence as “tantamount to life in prison.”

Rothstein wrote Cohn in March to say the “special security conditions of my confinement” made it difficult for him to communicate with his attorney, Marc Nurik, to prepare his legal response to the withdrawn motion. Rothstein typed his own response “using an extremely old typewriter.”

“Why would any criminal defendant enter into a plea agreement which could be interpreted as promising him nothing?” Rothstein asked Cohn.

The judge's order said Nurik agreed that prosecutors reserved the right to withdraw their motion, and “Rothstein was on notice of the potential consequences of his untruthfulness.”

Rothstein could have been in trouble for things close to home. His wife, Kim, pleaded guilty in 2013 to hiding more than $1 million worth of gems that had been withheld from federal agents, who collected all the fraud proceeds they could find.

Nurik, who has offices in Boca Raton and Los Angeles, said Wednesday that he hasn't had a chance to discuss the ruling with Rothstein and had no comment on the decision.

“Federal inmates typically have a lot of phone access, and they also have the ability to use email. There's no email system in his situation, and phone access is limited,” Nurik said. “I can't communicate with him within the normal channels.”