THE SLEEPING CAR MURDER (1965)
starring Simone Signoret, Yves Montand, Pierre Mondy and Jean-Louis Trintignant; based on a novel by Sébastien Japrisot; written and directed by Costa-Gavras
Six people travel by train overnight from Marseilles to Paris. When the train arrives at its destination, one of the passengers is found dead in a sleeping berth. The police investigate the other five passengers, suspecting that one of them was responsible.