A businessman who made $53,700 in illegal contributions to U.S. Sen. Robert Torricelli's campaign was sentenced to 18 months and one day in federal prison Thursday.

David Chang, the key government witness in the federal investigation into Torricelli's finances, was also fined $20,000 and barred from political or campaign fund-raising.

The sentencing is the last major event in the three-year investigation into the senator's finances, which closed in January without any charges against Torricelli. Prosecutors gave their material to the Senate ethics committee.

Chang spoke for five minutes, telling the judge he was used by Torricelli and rejecting attacks on his credibility. He asked for leniency.

U.S. District Judge Alfred M. Wolin could have given Chang probation and did find he gave substantial assistance to investigators. But Wolin noted that Chang undermined his ability to be called as a witness by his erratic behavior.

In a legal brief asking for leniency in sentencing, Chang said Torricelli urged him to lie to prosecutors and threatened his life.

According to the filing, Torricelli, urged Chang to leave the country rather than cooperate with the investigation and asked him to falsely claim the cash and gratuities were loans.

Chang also accused the senator of threatening him by talking about friends with organized crime connections and following him into a convenience store with a prominent waste disposal contractor.

"Senator Torricelli repeatedly warned him that his life would be in danger if he cooperated with the government," Chang's lawyer, Bradley D. Simon, wrote in the memorandum. "He specifically told Mr. Chang that he had friends in high-ranking positions within the Newark FBI who would frustrate any attempts to bring the investigation to the senator's level."

Torricelli's advisers denied the senator sought to prevent Chang from cooperating with the investigation and described the businessman as mentally unstable and a habitual liar.

They also said the senator felt vindicated by the fact that prosecutors decided not to file criminal charges in his case.

"Mr. Chang has a long history of making false accusations against public officials that included not only Senator Torricelli but also Attorney General Janet Reno and other high-ranking government officials," said Torricelli's spokeswoman, Debra DeShong. "Mr. Chang is a deeply troubled individual whose own lawyers have referred to his psychiatric problems."

Although Chang pleaded guilty nearly two years ago and agreed to cooperate with federal investigators, it is unclear how useful he was.

Of the five other donors who also admitted making illegal contributions, only one pleaded after Chang, a Frenchman who had been snared before Chang's plea on unrelated charges. Two other people pleaded guilty to non-finance charges.

Prosecutors also faced a great risk if they chose to take someone to trial and put Chang on the witness stand because he displayed an erratic demeanor during court sessions. No indictments were returned after Chang's plea.

Torricelli, who is running for a second term in November, has maintained he was unaware of any of the illegal contributions. He has said Chang was his friend, but became "every elected official's worst nightmare."