PRAGUE  Pavel remembers the violent night sweats two days before the murder. He went to see a family doctor, who said they would go away. But after viewing a Bruce Lee martial arts film, he said, he felt uncontrollable sexual desires. He invited a 12-year-old neighbor home. Then he stabbed the boy repeatedly.

His psychiatrist says Pavel derived his sexual pleasure from the violence.

More than 20 years have passed. Pavel, then 18, spent seven years in prison and five years in a psychiatric institution. During his last year in prison, he asked to be surgically castrated. Having his testicles removed, he said, was like draining the gasoline from a car hard-wired to crash. A large, dough-faced man, he is sterile and has forsaken marriage, romantic relationships and sex, he said. His life revolves around a Catholic charity, where he is a gardener.

“I can finally live knowing that I am no harm to anybody,” he said during an interview at a McDonald’s here, as children played loudly nearby. “I am living a productive life. I want to tell people that there is help.”

He refused to give his last name for fear of being hounded.

Whether castration can help rehabilitate violent sex offenders has come under new scrutiny after the Council of Europe’s anti-torture committee last month called surgical castration “invasive, irreversible and mutilating” and demanded that the Czech Republic stop offering the procedure to violent sex offenders. Other critics said that castration threatened to lead society down a dangerous road toward eugenics.