The movies might belong to years between 70’s to 90’s. It’s a crime movie.
French police force finds a sealed large dinning room where several dead bodies lied around a dinner table. Based on a video footage taken by killer himself which is found by police force in another room around the crime scene, killer poisoned their food and killed them all and left their bodies & video footage there, intentionally.
During the movie, we understand that killer was taking revenge and the vicitms were familiars who have done something bad to the killer. ( I cannot remember what they had done.) and police detective finds that he is still searching for other guys to kill them in order to complete his revenge process.
Lastly, killers goes to a live music concert and finishes off his last victim who was one of the orchestra’s musicians. Police arrests him, but he commits a suicide by taking a poisonous pill.
I’m not sure about its being french. I watched it when I was a kid. Maybe it was british.