Le monte-charge (1962)

On a Christmas night, an ex-convict, Robert Herbin, meets a beautiful Italian married woman Marthe Drévet, who has got a lot of things to hide. She lives in an old house, the first floor of which is a big workshop where a service elevator leads to the apartment. Marthe takes Robert to her home for a drink, he puts a small bird he bought on the Xmas tree, and they go for a stroll in the streets. When they come back, there's a dead body in the room (the husband) and most extraordinary thing, the bird has disappeared.