Animal (2007)

Europe, in the near future. Thomas, a molecular biologist, is researching human aggression. He meets an imprisoned monster—a serial killer named Vincent Iparrak. He pretends to study Vincent’s DNA, but he has another agenda in mind.

He instead injects a serum to supress aggressive impulsions. But when Iparrak awakes, the killer finds himself painfully aware of his past crimes and full of remorse, and puts an end to the experiment. With no other guinea pig available, Thomas uses the serum himself.