Dr. François Simon was one of the many people who knew that Joël Le Scouarnec had been convicted of downloading child sexual abuse imagery in 2005 and was continuing to operate on children as a gastric surgeon.

More than a decade later, the French police arrested Mr. Le Scouarnec. They would eventually charge him with the rape or sexual assault of 299 former patients, most of them children.

Dr. Simon was the head of an official board that oversaw doctors in Finistère, Brittany, where Mr. Le Scouarnec was employed in the late 2000s. He was among several people in France’s elaborately bureaucratic health system tasked with addressing Mr. Le Scouarnec’s initial criminal conviction.

Like many, in the end, he dropped the ball. He could have called for a disciplinary hearing, but instead, he sent the verdict up to the Ministry of Health’s departmental branch. He told a court this month that he had believed that office could address it more urgently. His own board voted almost unanimously that Mr. Le Scouarnec’s actions had not breached the medical code of ethics.

“We tried to do what we could,” Dr. Simon, who is now retired, said in a courtroom in Vannes, a Brittany port town, where he had been summoned as a witness against his will. “I can’t say there was a malfunction, but I regret it because there was a misunderstanding.”