Berserker

Berserker (2015) is a mystery, crime directed by Pablo Hernando rated 4.9/10.

Hugo Vartan is an author looking for a juicy story for his next book. He comes across one in the form of the sister of his flatmate's boyfriend, who has been hospitalised in a psychiatric ward for, seemingly, murdering her partner, beheading him with a knife and sticking his head on the steering wheel of her car.