Twilight

A former inspector is called in to investigate a child murder. A suspect confesses to the crime, but knowing that the confession came only after the man was browbeaten, the inspector's instincts tell him that the man is not the murderer and there is a serial killer at work. However, he is alone in his assessment and the case is closed. He is warned by a psychiatrist that the murderer he seeks might not exist, and he might drive himself mad with his obsession in finding the man... (Summary by Alex Watkins)