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Former WorldCom financial chief Scott Sullivan (search), the government's star witness at the criminal trial of Bernard Ebbers (search), was sentenced Thursday to five years in prison for his role in the largest accounting fraud in U.S. history.

Sullivan, 43, pleaded guilty to conspiracy, securities fraud and making false financial filings. He cooperated with prosecutors probing wrongdoing at WorldCom in hopes of receiving a reduced prison sentence.

Sullivan became the fifth WorldCom executive to be sentenced to prison for the $11 billion fraud. His sentence is topped only by that of Ebbers, who got 25 years.

Sullivan was the star witness at Ebbers' trial earlier this year, testifying the CEO repeatedly instructed him to "hit the numbers" — or adjust WorldCom's books to meet Wall Street expectations.

Sullivan told the court he was "ashamed and embarrassed."

"I made horrible decisions," he said. "It was a misguided effort to save the company. ... I ask for leniency so I can get back to my family as soon as possible."

"Mr. Sullivan was the architect of the fraud at WorldCom," said Manhattan federal judge Barbara Jones, who ordered him to report to prison Nov. 11.

During Ebbers' trial, Sullivan, in more than 30 hours of testimony, said he repeatedly expressed his reservations to Ebbers about cooking the books but was overruled by his boss.

"I told Bernie, 'This isn't right,"' Sullivan said, describing an October 2000 meeting in which he said he showed Ebbers a plan to improperly create $133 million in revenue. "He just stared at it, and he looked up at me and he said, 'We have to hit our numbers."'

Sullivan has already agreed to sell the $11 million mansion he is building with his wife in Boca Raton, Fla., to settle a lawsuit brought by former WorldCom shareholders.

The house is a lavish, 30,000-square-foot, Mediterranean-style mansion with 10 bedrooms, nine bathrooms and seven fireplaces made of carved stone and mahogany.

WorldCom collapsed in 2002 when the fraud came to light. It has since emerged under the name MCI Inc. (MCIP), which is being acquired by Verizon Communications Inc. (VZ).

On Wednesday, former WorldCom controller David Myers (search), who admitted playing a pivotal role in the fraud, was sentenced to one year and one day in prison.

On Tuesday, WorldCom's former director of general accounting, Buford "Buddy" Yates (search), 49, was sentenced to one year and one day in prison.

Last week, Betty Vinson, a former WorldCom accounting official who said she pulled some numbers "out of the air" when she helped fudge company books, was sentenced to five months in prison.

Another former accounting official, Troy Normand, was sentenced to three years of probation after a federal prosecutor said his role in the fraud was less than Vinson's.

Reuters and the Associated Press contributed to this report.