Hitchcock famously heaped much of the failure of I Confess on star Montgomery Clift, the self serious method acting, the boozing that showed up in the glazed over eyes. They’d never make another picture together.
However Clift is the best thing in I Confess as a young priest who finds the refugee he helped place in the community has committed a murder. Since he discovers this through a confessional he is bound by faith not to divulge either the details of the crime or that the confession happened at all. There’s only the minimum of explanation as to the rules of Catholic confessionals, and that’s all that’s needed. The rest is sold on Clift’s face.
Tormenting Clift throughout the picture are Karl Malden as the police inspector who eyes the young priest with intense suspicion on first sight. All subsequent evidence is twisted against the priest with a wide-eyed fury. His compliment comes from Otto Hasse, the degenerate (vaguely German) refugee who finds it increasingly convenient to frame his benefactor for his crime.
The biggest villain in this picture is Hitchcock himself, and he commits no graver error than grafting an extended flashback into the heart of the film and leaving its narration to a typically ill-suited Ann Baxter. Rather than go with the original ending that would’ve sent Clift to the gallow’s pole, Hitchcock instead finds room for a shootout (supposedly to preempt any censorship) that flies in the face of the point of the film.
This same ground was covered much more successfully in Bresson’s “Diary of a Country Priest”. There too a priest could save himself a great deal of social shaming if he’d admit what was divulged in a confession. Both priests are surprisingly comfortable with the prosecution by their communities for crimes on which they’re innocent. Though never explicitly stated both even welcome the unjustified scorn. There’s no higher ideal for a Catholic than getting thrown to the lions.