Robert J. Halderman is shown Oct. 2, 2009, in state Supreme Court in New York. He has been released from jail after serving four months for trying to extort $2 million US from David Letterman. Robert J. Halderman is shown Oct. 2, 2009, in state Supreme Court in New York. He has been released from jail after serving four months for trying to extort $2 million US from David Letterman. (Associated Press)

The former television producer who tried to blackmail late-night talk show host David Letterman over his sexual affairs was freed Thursday after four months in jail.

Robert "Joe" Halderman was given a six-month sentence after pleading guilty to attempted grand larceny for trying to extort $2 million US from Letterman.

Halderman was given time off his sentence at Rikers Island in New York for good behaviour, according to his lawyer, Gerald Shargel.

He has to complete 1,000 hours of community service and will be training people who had been homeless or recently released from prison for the job market. He also will be on probation for five years.

Halderman is no longer employed by CBS, but he has been nominated for a news and documentary Emmy Award for his work with the program 48 Hours.

He is one of four producers cited for an April 2009 story about an American exchange student charged with murder in Italy.

Halderman's extortion attempt was prompted in part by jealousy, Shargel said. He had learned from his girlfriend's diary that she had had an affair with Letterman.

After his extortion attempt on Letterman, the Late Show host revealed on air that he had had affairs with his staff.

A spokesman for Letterman declined to comment on Halderman's release.

With files from The Associated Press