Alfred Hitchcock knew a thing or two about complicated thrillers.

Having a murderer confess to a priest -- who couldn't betray this trust -- was already a familiar plot twist by 1953, when Hitchcock released "I Confess." Because of the seal of confession, this noble priest couldn't even clear his own name when police suspected that he was the killer.

Good prevails in the end. Shot by police, the killer makes an urgent final confession to the priest.

"It's natural for a Catholic filmmaker like Hitchcock to see the dramatic potential of confession, with its combination of mystery and holiness," said film critic Steven D. Greydanus, best known for his work for the National Catholic Register. "At the same time, Hitchcock thought 'I Confess' was a mistake, because he thought that his mostly Protestant audience in America just wouldn't get it."

The sacrament of confession is both sacred and secret -- facts known to Medieval playwrights as well as modern filmmakers. Thus, putting a confession rite on a movie screen is a "transgressive act" of the highest kind, said Greydanus, who serves as a permanent deacon in the Diocese of Newark, N.J. (Deacons do not hear confessions.)

 "Voyeurism is an important theme in much of Hitchcock's work and he knew that using confession in this way was a kind of voyeurism. … He knew this was a kind of taboo."

 Nevertheless, Hollywood scribes have frequently used confession and penance for everything from cheap laughs ("A League of Their Own"), to shattering guilt (Godfather III), to near-miraculous transformations ("The Mission"). In a recent 6,000-word essay -- "In Search of True Confession in the Movies" -- Greydanus covered a century of cinema, while admitting that he had to omit dozens of movies that included confession scenes.

The key is that filmmakers struggle to capture, in words and images, what is happening in a person's heart. The act of confession opens a window into the soul, since characters are forced to put their sins and struggles into words.

"Perhaps the very secrecy surrounding the sacrament of confession was part of what attracted filmmakers to depict it," wrote Greydanus. "Anyone can witness the Eucharistic liturgy, an ordination or a wedding. … 

“But what transpires in confession can only be imagined -- which is the cinema's stock in trade. … Often enough, confession scenes have served in movies as a pretext to allow a character to articulate their spiritual or temporal struggles, whether or not any kind of sin is involved."

On-screen confessions frequently show dramatic plot twists and unusual confessions -- such as a man's pronouncement, in the 2014 drama "Calvary," that he will kill a brave, faithful Irish priest. Father James Lavelle doesn't report this death threat to police, of course, because it occurred during confession.

The rarest of onscreen confessions, noted Greydanus, is actually the most common form of the sacrament -- believers confessing ordinary sins as they struggle to follow their faith at work, in their homes and in private life.

There are a few glimpses of ordinary confession, as in the 1987 comedy classic "Moonstruck." In one scene, a confused character confesses, between lesser offenses, "Once I slept with the brother of my fiancé." In the final scene, the family matriarch demands that her unfaithful husband end an affair. When he agrees to this, she immediately adds, in a dead-serious voice: "And go to confession."

Greydanus also praised the 2016 comedy "Hail, Caesar" -- by the Coen brothers, Joel and Ethan. This satire explores the sins and foibles of various Hollywood players during the filming of a biblical epic in the golden 1950s. 

The central character is a Hollywood "fixer" -- Eddie Mannix -- who attempts to protect the public images of A-list stars. While most of the characters are quite ridiculous, he is shown to be a sincere Catholic who keeps returning to confession while wrestling with workaholism, his smoking habit and minor weaknesses as a husband and father.

"It's hard. But I'm trying," he tells his priest.

"This is what confession is about for most people," said Greydanus. This winsome character "confesses his sins and he is forgiven. Eddie Mannix is a decent man and he is struggling with the chaos in the world around him. It's hard and he knows that he needs help."