The film also shows interviews with his parents, who are divorced; his federal public defender, Julia L. Gatto; a juror; and various psychiatric, legal and Internet experts. One expert, Lee Rowland, an American Civil Liberties Union lawyer, says, “The cannibal cop case really raises the big question: What is the line between thought and action, right, between fantasy and crime? And it’s so gray.”

Mr. Valle, who was fired from the Police Department upon his conviction, did not testify at trial and made only brief comments, including an apology, outside the courthouse. In the film, he appears relaxed and not defensive. There are “a lot of myths” about his case, he says, adding, “I want everyone to have all the facts in front of them before they make up their minds.” He seems at a loss, though, to explain why he acted as he did.

“I mean, yeah, I had a stressful job, but I don’t know how much that played into all that,” he says. “You know, I could have gone out and got drunk. I could have stayed up and watched TV.” Perhaps the “most important thing” he got out of the chats, he says, “was just acceptance.”

“This is the first time I’m really opening up about all kinds of freaky stuff, you know, cannibalism and bondage. All these years, it’s all bottled up. Here, I had my chance to finally talk to somebody about it.

“It was such a relief to get it off my chest. When you’re typing it, you don’t really think about it. You’re just sort of in the moment.”

But, he adds: “I’m incapable of any violence. I couldn’t hurt a fly.”

Mr. Valle says that he was a good husband and father and that he did well at work. His wife has since divorced him, the film says. Mr. Valle claims that just when he decided to “delete everything” from his computer, his wife installed software that allowed her to monitor his activities and ultimately discover his writings. “If I had done it a day sooner,” he says, “none of this would have happened. Isn’t that incredible?”

He suggests the government pursued the appeal “just to save face.”

“They’re smart people; they have to know I’m innocent,” he says. “They have to know there’s no evidence. They have to know they screwed up.”