U.S. District Judge Laura Swain Wednesday sentenced a fourth former Bernie Madoff aide to a fraction of the prison time called for by the government, probation officials and federal guidelines, but got some blowback in a testy exchange with a prosecutor.

"Your honor has shown extraordinary mercy," Assistant U.S. Attorney Matthew Schwartz told the judge before she sentenced Madoff computer programmer George Perez. "But we ask, on behalf of the victims of this fraud, for justice."

"I know you're looking at the 17th floor across the road," Swain responded sarcastically, referring to the federal appeals court where prosecutors could seek review of her sentences. "I shall eagerly await the newspaper reports of the sentences on appeal."

Swain eventually sentenced Perez, who oversaw production of phony reports used to fool the Securities and Exchange Commission and client auditors, to just 2 1/2 years in prison. Federal sentencing guidelines called for him to get 100 years, the court's probation office urged 8 years, and prosecutors wanted more than 8 years.

The 30-month term for Perez, 48, of East Brunswick, New Jersey, fit a pattern of leniency Swain set this week in sentencing ex-Madoff aides who went to trial and were convicted of 31 counts of conspiracy and fraud for their roles in the $20 billion Ponzi scheme.

Former director of operations Daniel Bonventre of Manhattan got 10 years instead of over 20 sought by the government. Annette Bongiorno of Manhasset, Madoff's ex-secretary, got 6 years instead of 20, and computer manager Jerome O'Hara of Malverne got 2 1/2 years instead of 8.

All the defendants plan to appeal their convictions. Despite the judge's prediction, prosecutors have not signaled if they will appeal her sentences. Appeals courts give trial judges great latitude in sentencing, and rarely overturn their decisions.

Schwartz said O'Hara and Perez acknowledged in a 2006 letter that they were "uncomfortable" with the phony reports they were being asked to produce -- but kept working for Madoff and earning a lucrative salary until the firm collapsed in 2008.

He warned that for years to come, "small time crooks" would be using Swain's 2 1/2-year Madoff sentences to argue for less time in any case that didn't involve billions of dollars.

"Three years, $20 billion, thousands of victims -- that is, all by itself, a crime of unprecedented magnitude," he told the judge. "A sentence of 2 1/2 years is not reasonable, not just, not reflective of the seriousness of the offense and not consistent with other sentences."

Swain, as she has all week, said that the aides facilitated Madoff's scam but didn't know it was all a Ponzi scheme, and she would not sentence them as if they were Madoff himself.

She also imposed a $19.7 billion forfeiture order on Perez, and pointed out that he has been under a curfew since his 2009 arrest and will be under house arrest for a year after he is released.

"This," she said, "is not merely a 2 1/2-year jail term."

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