Roman Polanski, the film director, is using a film being shown at the Sundance Film Festival to prove that 30-year-old sex charges against him should be dropped.

Polanski, who fled the US in 1978 after being found guilty of having sex with a 13-year-old girl, claims that the documentary proves "a pattern of misconduct and improper communications" between the LA Country district attorney's office and the judge presiding over his case.

His lawyers have filed a request to have the charges dismissed because of judicial and prosecutorial conduct.

"This case serves as a classic example of how our justice system can be abused, and defendants' rights trampled, by an unholy alliance between courts and criminal prosecutors," said a statement from attorneys Chad Hummel and Brad Dalton.

Times Archive, 1977: Hollywood director charged with rape

According to police, the alleged assault happened at the home of the actor Jack Nicholson

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Mr Dalton is the son of attorney Doug Dalton, who represented the acclaimed film maker in the original case.

Polish born Polanski, 75, has been living in self-imposed exile in France since 1978, after sensationally pleading guilty to unlawful sexual intercourse with a minor.

An arrest warrant for him is still in effect, barring him from re-entering the US although the now 43-year-old woman with whom he admitted having sex has said that she wants the charge dropped and that he should be allowed back into the US.

The new effort to wipe out the charge comes in the wake of an HBO documentary, "Roman Polanski: Wanted and Desired," which portrayed Judge Laurence J. Rittenbrand, who presided over the trial, as a publicity seeker who held news conferences and engaged in extra-judicial meetings about the case.

In their brief, Mr Polanski's lawyers quote liberally from the documentary, citing statements by former Deputy District Attorney David Wells in which he acknowledged advising the judge on how to sentence the film director, even though he was not assigned to the case.

The lawyers said that Mr Wells' recommendation to send Polanski away for a diagnostic study was illegal without his lawyers present. They said Mr Wells also inflamed the judge by showing him photos depicting the director with girls at an Oktoberfest party in Germany while he was awaiting sentencing. They said the photos were misrepresented.

"As the result of DDA Wells' illegal ... communications, Mr Polanski has been subject to a punishment that has spanned the course of over 30 years," the motion stated, noting he has been deprived of opportunities to work on films outside France.

Polanski has continued to direct films while in exile, including the 2002 Holocaust drama 'The Pianist,' for which he won the best-director Academy Award.

Sandi Gibbons, spokeswoman for Los Angeles District Attorney Steve Cooley, said her office had not been served with the motion and heard about it only through media reports. She said the office could not take a position until they see the legal papers.

"We're looking forward to seeing Mr Polanski in Los Angeles to litigate it," she said.

A hearing on the matter is scheduled for January 21 in Los Angeles County Superior Court.

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