Le Monstre aux filles (1961)

The new science teacher Dr. Julian Olcott with a mysterious past arrives in an institutional boarding school for troublemaker girls. Along the night, the intern Mary Smith, who is blackmailing another teacher - Sir Alfred Whiteman - with some love letters, is slaughtered by a werewolf. The detective in charge of the investigation attributes the crime to a wolf, while her mate Priscilla believes she was killed by Sir Alfred. On the next days, other deaths happen in the school, reducing the list of suspects.