Original title (FR): Le Fil (The Thread)

Jean Monier (Daniel Auteuil) is a disillusioned lawyer, appointed to defend Nicolas Milik (Grégory Gadebois), a man accused of murdering his wife. While everything points to his guilt, Monier takes up the case, convinced of his innocence.

https://www.themoviedb.org/movie/1136394-le-fil