A detective movie about a murder of a guest who blackmailed

Looking for a single detective movie. Only watched the beginning of the movie. Anyway, a certain girl from a good family corresponds with a guy from prison. After he finishes his sentence, he comes to visit her. The girl's parents are rich and have a whole castle. During a conversation at the table, it turns out that the guy had an accomplice, but the accomplice escaped and the guy was locked up for him. When the girl's parents asked why he didn't turn in the underling, the guy said to blackmail him. Then the girl took the guy to the guest house, at which point her brother tells her parents that the underling was him. The guy in the guest house tries to grope the girl and in response to her outrage and a promise to kick him out of the castle says that he would then pawn her brother off and in general they are now on the hook for him. At night someone kills the guy. A detective arrives to investigate, seemingly a famous artist and seemingly French, but I'm not sure. A knife is missing from the kitchen, which was probably used to stab the guy, and the knife is nowhere to be found. The detective starts questioning everyone and admires the girl for being so smart and good. The movie seems to be in black and white, but I'm not sure. The detective seemed fat and a man in years. There was also a computer on the girl's desk, only an old model with a bandura monitor.