Moenchengladbach, Germany - A convicted rapist, 38, voluntarily returned to prison on Friday, a day after judges rejected a call to place him in preventive detention, a German justice official said.

The man served out a 1999 sentence of nine-and-a-half years for raping several under-age girls, and psychologists warned he might offend again. But the court said there were no grounds to detain him after the term finished.

The man is free to leave the prison in the city of Moenchengladbach, where he is now staying as a guest of the state, at any time.

"With full knowledge, he is accepting help from the prison so as not to spoil the outcome of his therapy," said Andrea Boegge, a justice department spokesman in North Rhine Westphalia state.

He is to continue a course of behavioural therapy, after admitting he finds it difficult to suppress fantasies of violent rape.(dpa)