This documentary by Erin Lee Carr, a first-time feature filmmaker whose shorter work includes the Vice short film on 3-D printed guns, explores another high-tech, Internet-era issue in which culpability and guilt are difficult to assess. In Thought Crimes, it’s the story of New York cop Gilberto Valle, who was convicted in 2013 as “the Cannibal Cop,” charged with conspiracy to abduct, torture, cook, and eat many women, including family friends, former schoolmates and his own wife. He was caught, tried, and convicted before he could carry out any of his despicable plans — but were they actual plans, or just twisted fantasies described and shared on the Internet? The question of when, and whether, a person should be prosecuted for what he thinks is at the heart of this study, which keeps flipping to the other side of the coin, and should keep you thinking until, and after, the end.