GENEVA  Roman Polanski’s repeated claims that there was misconduct at his trial for having sex with a 13-year-old girl in 1977 ran into a brick wall in American courts. But they were enough apparently to convince Swiss authorities that he should walk free.

Switzerland announced Monday that it would not extradite Mr. Polanski, a famous film director, to the United States in part because of fresh doubts over the conduct of the judge in his original trial.

“He’s a free man,” the Swiss justice minister, Eveline Widmer-Schlumpf, said at a news conference on Monday.

The ruling means that, after nearly a year of courtroom wrangling in the United States and Switzerland, the case is roughly where it has been for decades: Mr. Polanski is free to return to his home in France but remains wanted in the United States. He was arrested at the Zurich airport last September on an international warrant issued by the United States on charges including rape and sodomy dating from 1977. In December, the Swiss authorities allowed him to move to his chalet in the ski resort of Gstaad under house arrest on bail of $4.5 million pending a decision on his extradition.