Love Letter of a Murderer
Carta de amor de un asesino (original)
A man (José Luis López Vázquez) walks into a bar and shoots four people dead. Next day everybody is talking about the murders. The police know who the killer is and have his photo, but the man himself remains at large. Blanca (Serena Vergano), a lonely librarian, receives a letter from him, declaring his love for her. Apparently he has been a regular at the municipal library, although Blanca denies ever having noticed him.
Starring Serena Vergano, Rosa María Mateo, José Calvo, Manuel Tejada, Alejandro López, Marisa Porcel, Vicenta Roca, José Luis López Vázquez
Watch "Love Letter of a Murderer" on FlixOlè released in 1972. It's a drama and horror movie, and has a rating of 6 out of 10 from Imdb which is fairly okay for this kind of movie.