Mr. Sugaya, now 63, has become a national figure, and perhaps the country’s most vocal critic of forced confessions  a recurring problem here. He has written or co-written three books, including one titled “Falsely Convicted,” and tours the country giving talks about his experience.

“I tell people not to believe the police,” said Mr. Sugaya, a small, slightly built man whose face seems almost hidden behind a large pair of wire-rim glasses. “Look what they did to me.”

Indeed, with slumped shoulders and an almost cowering demeanor that brings to mind a frightened animal caught in car headlights, Mr. Sugaya seems as unlikely a crusader against the abuse of power as he did a serial killer. But he can be disarmingly open, and his voice exudes a quiet confidence that he says he acquired in prison, where he learned to fend for himself.

During those years, he said, he met other convicts who told him they had been convicted because of false confessions. He said a desire to help them and others is one reason he has embraced his newfound celebrity, though he remains visibly uncomfortable with all the attention.

“I want to go back to my quiet life of before,” Mr. Sugaya said. “But when I think that others have suffered the same treatment as me, I want to work to help them.”