What is the scariest true crime documentary?

One of the scariest true-crime documentaries for many viewers is The Act of Killing. It’s not scary in a jump-scare way; it’s disturbing because real perpetrators of mass murder calmly reenact and justify what they did, which makes it feel psychologically horrifying and morally unreal.

If you mean “most terrifying to watch alone at night,” that’s subjective. For true crime specifically, The Jinx, Dear Zachary, and The Imposter are also deeply unsettling, but in different ways.

The Nightmare is frightening too, but it’s not true crime.