The jailhouse informer who exposed a plot to kill and behead a Long Island federal judge and prosecutor lost his bid to get out of prison immediately at his sentencing Monday in federal court in Brooklyn.

U.S. District Judge John Keenan said career criminal Gerald Machacek, 44, described as the "Babe Ruth of cooperators" by his attorney for exposing the 2012 plot by coin dealer Joseph Romano of Levittown, will still have to serve another year behind bars.

"I know you wanted to walk out of here today," Keenan told Machacek, who also was lauded by prosecutors for helping save two lives. "But in view of your record, I didn't think that was something I could do."

Romano met Machacek in 2012 at the Nassau County jail, where, he would later testify, Romano discussed taking revenge on U.S. District Judge Joseph Bianco and prosecutor Lara Gatz for a 15-year sentence he received in a coin fraud case.

Machacek alerted authorities, who videotaped a later staged meeting between the two. He agreed to put Romano in contact with a "hit man" who was actually an undercover police officer. Romano claimed he was entrapped, and called Machacek as a witness at his trial in January.

Federal sentencing guidelines called for Machacek to serve between 100 and 125 months in prison after pleading guilty to robbery, conspiracy and weapons possession charges.

He had accumulated 18 convictions on theft and other charges since age 12, according to his lawyer, and had been jailed for 30 months on the federal charges. Keenan sentenced him to 42 months, giving him another year to serve, and then 5 years on probation.

Prosecutors urged leniency based on his cooperation against both Romano and other members of the robbery crew he was charged with. Defense lawyer Anthony LaPinta said his actions had put Machacek and his family in peril.

"Maybe you could call him the Babe Ruth of cooperators," LaPinta said. "I don't see how anyone could give more service to the government than what Mr. Machacek has done."

Machacek, who grew up in Queens and was living in Brooklyn before his latest arrest, told Keenan that his life of crime was over.

"For once in my life I did something good," he said. "This has been a defining moment for me to do good and not to do bad."

"I do think some prison time is necessary because of your record," said the judge, who added a farewell as Machacek flashed a look of disappointment to his wife.

"Good luck, Mr. Machacek," Keenan said.

Romano was sentenced to life in prison in April.

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