10 More Horror Movie Characters Who Didn't Know They Were The Killer

Session 9 follows protagonist Gordon Fleming (Peter Mullan), the owner of an asbestos clean-up company who heads to an abandoned psychiatric hospital with his crew for his latest job.

Things get increasingly creepy and unsettling throughout the film, and though the audience is steered in several directions once the bodies start piling up, it's ultimately revealed that the killer was unknowingly Gordon himself, who killed his colleagues while in a dissociated state.

It's additionally revealed that Gordon killed his own wife and daughter following a household accident prior to the job.

However, it's left ambiguous as to whether Gordon simply snapped of his own accord or was actually possessed by Simon, a malevolent alternate personality of one of the hospital's previous patients who preys on "the weak and the wounded."

Gordon proves ignorant enough of his own brutality that he even tries to call home in an attempt to apologise to his dead wife, seemingly unable to come to terms with the violence he has committed.