The Golden Glove aka Der Goldene Handschuh
https://www.imdb.com/title/tt7670212/This movie was fucked up. I randomly came across a review of it, and it basically described it something more than "torture porn". I usually can't stand movies like that, but this one caught my attention after reading about it more. Most of the reviews were extremely positive but extremely cautionary.... like 'this will stay in your head for days, so disgusting you will need to shower after', etc...
It was a pretty good movie, but wasn't nearly as disturbing as I was expecting. I liked it because it was a far more realistic take of the 'serial-killer' genre. I can't stand the hollywood-style serial killers... you know, the diabolical college professor who outsmarts law enforcement with supreme intelligence. It's made up movie shit.
This is based on a true story, and really emphasizes the filth and depravity these types truly live in. It really is a disgusting movie, and not really the violence... just the existence. Some pretty abhorrent sex scenes. It didn't burn into my head like when I watched Irreversible or Man Bites Dog, but it's still pretty rough.