Help me - French/Italian movie

[Weiss]

Hi everyone,
Please help me with the following movie. Thank you very much.
The settings is probably before WW2 (1920 1930s looking cars). Movie is about a criminal who befriended a couple. Then he killed the husband for some reasons. The wife then did the investigation and then came to confront the criminal, pointing gun at him. However, he had already drugged her drinks so she fell asleep and was captured by him. She then pretended to agree to become his girlfriend to find a way for revenge. Then one day she managed to tell the police, but was discovered by the guy and strangled to death before the police could arrive.

[David_Locke]

If most of the film happens on a sailing boat off the italian coast, it could be Plein Soleil / Purple Noon (1960) René Clément.