Dead Certain (1981)

Commissioner Servolle (Claude Brasseur), 40, is the undisputed ace of the criminal. He is a man who knows how to impose himself wherever he goes and better yet, to make himself loved: One day, another happiness arrives: friendship. The chosen one is called Faguet (Jean-Louis Trintignant), a famous architect always happy and full of humor. But this event falls perfectly well to boost the morale of Servolle, because for 8 months, he has been trampling on the case of the killer of the beautiful neighborhoods: a maniac who coldly slaughters women. He has already knocked three times and the fourth is terrible because she is Faguet's own wife. Servolle is now at the start of the track. He knows he will have the killer. But suppose that Faguet at the beginning of their friendship introduced him to his mistress as his legitimate wife, suppose that he was once a sniper, and that in the Faguet couple, hatred had reigned for years. A long nightmare will then begin for Servolle. If he kept a bit of lucidity, he would compare it to a desperation of love or, perhaps worse, friendship.