What's the most interesting documentary you've ever watched?

I feel triggered just thinking about it. Its the first and last documentary that i've ever watched it was called, Gladiator Days: Anatomy of a Prison Murder. I cried for days i was so traumatized. It was about a racially motivated murder that occured at the Utah State Prison. I just kept thinking about the victim's family about his mother and how she has to relive this moment of her son's brutal murder.