Let's start with a couple of prison documentaries.
My favourite is probably Inside Death Row With Sir Trevor McDonald.
It features many long interviews with several death row and lifer inmates in Indiana State Prison. The documentary spends lots of time letting you get to know and humanizing the inmates, only to then hit you with the truth of what exactly they did to get the death penalty to begin with. Trevor McDonald openly says he is against the death penalty, but ends up telling one of the inmates directly to his face that after hearing what he did he understands why people are for it. It has a sequel, Death Row 2018, which follows up with some of the prisoners 5 years later as well as features some new inmates, including a recently caught serial killer.
Another one I love is The Condemned, a BBC documentary about Penal Colony 56, better known as Black Eagle (not to be confused with Black Dolphin), one of the most infamous prisons in Russia, a former gulag that was recently closed due to its lack of basic things like toilets.
The documentary features no commentary. The only people you hear speaking are the prison guards, prisoners, and the family members of the prisoners. They tell the stories of how they got arrested, what they do to pass the time in prison, their opinions on the abolishment of the death penalty, and what it's like to drive 7+ hours through desolate frozen wastelands just to see your son for an hour once per year. It's haunting.
And to finish off, the most disturbing documentary I have ever seen. 被曝治療８３日間の記録～東海村臨界事故～ (83 Day Record of Treating Radiation Sickness -The Tokaimura Criticality Accident-), by NHK.
1999年の東海村臨界事故で大量被ばくした大内久さんの治療に関するドキュメンタリー番組です。
www.dailymotion.com
It details the slow and absolutely horrific death of Oouchi Hisashi, the most radioactive man ever, over 83 days of pure hellish torture as doctors try in vain to keep him alive and his children try to cheer him on and tell him to hang in there. Since 2010 it has become difficult to find Japanese sources on the event online due to privacy complaints having been issued and sources including the names of the victims getting scrubbed from the Japanese-speaking Internet. The documentary contains the only publicized images of the victim; any other images purporting to be of the victim are actually from an American burn ward.
