“The Ritual,” with Al Pacino and Dan Stevens as Catholic priests, dramatizes the most thoroughly documented and widely publicized exorcism in American history.

For the film’s co-creator and writer-director David Midell, this third feature is, “Subject matter that asks questions about what people are willing to do to help those who are vulnerable around them.

“At its heart,” he said in a phone interview, “this is really about a group of people who come together to help a very, very vulnerable woman. And in the process, they put themselves at physical, spiritual and psychological risk.”

It was the fall of 1928 when Father Joseph Steiger (Stevens) of Saint Joseph’s parish in Earling, Iowa, was asked to assist in the exorcism of 46-year-old Emma Schmidt (Abigail Cowen) who had suffered for years with blackouts and an aversion to holy objects.

He would assist Theophilus Riesinger (Pacino), a Capuchin friar with a history of exorcism.

“We wanted a docudrama approach,” Midell said. “Use the real names, the real location. Al’s Theophilus Riesinger was actually profiled in Time magazine in 1936.

“Our primary source to develop the screenplay was a document called ‘Begone Satan,’ which was originally written in German. It was written by the Catholic church and based on the notes from Father Theophilus and Father Steiger about what happened.

“That document ‘Begone Satan’ is now used by the Catholic Church as a training tool for exorcists.”

As to how you get a legendary, Oscar-winning actor to star in your low-budget movie? You begin by giving him the script.

“I remember when the producer called me and said, ‘Al wants to meet and talk about the script.’ Of course, his reputation, his stature in the business, precedes him. So I was very nervous but within 10 or 15 minutes of us sitting down, it became two people talking about these characters and the story.

“He came with notes on the script, written in the margins. Post-it notes throughout asking questions. Clearly, he had read the script multiple times, done his homework, really thought about the character.”

As for Pacino’s accent in “The Ritual”?

“Theophilus Riesinger was born and raised in Bavaria, in southern Germany. He emigrated to the United States in his early 20s. I can’t remember if he did his seminary training in the US or in Germany — but we talked about the accent in our first or second meeting.

“We knew it made sense for the character to have some type of accent and Al did a really beautiful job of suggesting that this person had been in America for a long time, spoke multiple languages.

“You can hear Al’s character speak multiple languages in the film, as somebody who really had their roots in German and Germany.”

“The Ritual” opens Friday