Seifuku nusumi Dori Ma: gekisha naburu (1990)

A high-school girl with a hobby of documenting stuff with her video camera films a woman getting raped in a dirty alley. She get in contact with the rapist and start blackmailing him to let her film when he assaults his victims, whom he chooses because they are all patients of his psychologist sister, and he's been eavesdropping on their sessions.