Other mistake: The "Ten Killer" slashed Katherine Hourback's face/head close to 50 times (off-screen), leaving her face covered in blood. When Dan found Katherine's body in his front yard, there was diluted blood on her face (mostly left side), but no indication that she had been slashed with a utility knife about 50 times. Also, during the slashing, the Ten Killer's "aim" seemed off (too high for a victim sitting in a chair and with no adjustment for how her head might move after each forceful blow). (00:45:05 - 00:46:53)
Other mistake: At the very beginning when Riley shots the dude in the head, the blood comes out but the bullet does not break the glass.
Other mistake: While Amy speaks with Bilel through Skype, each time Bilel is in the Internet cafe the same guy is sitting behind him.
Other mistake: While "dead" Mike is bent over his car's engine, his left leg moves. (00:32:40)
Other mistake: During the murder in the stairwell, an old woman opens her apartment door outward, and Varg kicks it shut. Apartment doors always open inward, as did Euronymous' apartment in the same building.
Suggested correction: Euronymous' apartment door opens outward into the hallway, at least in the final scene it does when he's trying to get away from Varg.
Other mistake: The man who shows Kurt around the Dusseldorf Art Academy (and later becomes his friend) introduces himself as Harry Preusser, but during the end credits, his name is listed as Gunther Presseur. (01:54:25 - 03:04:00)