This is a thoughtful film, rich in implication. It begins in a bedroom, which is being monitored by some police agency, we don't know who. They have the room bugged, and under camera surveillance, and a hit man still manages to do his job. We learn as the film goes on that this hit man is effective precisely because he studies his subjects, gets to know them so well that he can think like them. Deep sympathetic powers are the source of his deadly capabilities. This element is doubled in the cop assigned to stop him - another student of human nature, who uses observation and intuitive sympathy to predict the hit man's moves. Each of these characters is profoundly able to be intimate with the object of his quest. The development of the bond between the hit man and the woman he loves works out this theme of intimate knowledge and sympathy on a parallel plane. The psychological truth of this keeps us entranced by the film despite some elaborate technological machinations (the hit man's wall of fire, for example) that would normally defy credibility.
