I am quite a fan of dark documentaries, in particular, mysteries. Below are some I have seen recently and some notes, if anyone has any to add or has seen the below would be interested to hear your thoughts, apologies if I have posted this before!
Making a Murderer (obviously) - the first season was more gripping than the second, not sure if this was because we know the current situation so the second season was less of a mystery but it did add more food for thought so was worth a watch.
Evil Genius - This one was interesting, started very dark, bit of an anti-climax as there's not as tight a conclusion as I would have liked but well worth the watch.
The Confession Tapes - I've only seen one or two of these so can't comment really, will need to watch some more.
The Jinx - This one started slow but ends very well so worth sticking with it.
The Keepers - I wasn't as big a fan of this as the above but still worth the watch.
Paradise Lost - this is a documovie, there is a trilogy of them. I watched half of the first one last night before falling asleep so will finish it later this week maybe. The half I saw was a bit of a mish mash of poor editing and interviews but the reviews are good and the story is chilling so will stick with it.