Alice Sweet Alice(1976).
Superb giallo-esque horror/thriller set around the Catholic church.
Brooke Shields plays Karen, a young girl having her first communion who ends up brutally murdered in church by a maniac donning a yellow mack and a mask. All the evidence points to Alice, her jealous and disturbed sister who was the last one to enter the church.
Directed by Alfred Sole, this has influences from several films, to Don't Look Now, Psycho, and even Halloween.
Paula Sheppard is superb as well as the extremely confused and disturbed young Alice. The rest of the cast are pretty good too with a memorable performance from a very creepy landlord.
Very well recommended. The atmosphere in the film is superb and steeped in religious iconography and gives a creepy feeling of unease. And a film with some extremely brutal and realistic murders. 8/10.