From The Depths Of Depravity: Forgive Me Father For I Have Sinned 2004 one on netflix

Father Frank, a devoted priest, discovers the secret diary of his friend, Father Richard, which describes his strange double life. Father Richard is a highly respected priest and counselor at an all boys’ college. But in the shadows of insanity he is a psychopathic serial killer responsible for the strangulation murders of over 80 young men and boys. The diary recounts his troubled childhood and adolescence and the circumstances which lead to his sick transition from a loving father figure to a perverted masked maniac.