Hollywood screenwriter and director Scott Derrickson is no stranger to terrifying storytelling centered on the demonic. Now, he’s preparing for the release of “Deliver Us From Evil,” a new film about an NYPD cop who battles supernatural forces.

Derrickson, who also directed 2005′s “The Exorcism of Emily Rose,” told TheBlaze this week that the process of making the film ended up being “the most disturbing time” in his career.

In preparing the screenplay more than a decade ago, he watched countless videos showing real-life exorcisms and other terrifying materials related to ex-cop Ralph Sarchie’s demonology work.

“I saw a lot, I heard a lot and read a lot of cases in a very concentrated period of time back then. I think it was a little bit of an overload. It was very oppressive,” Derrickson said. “Of all the things I’ve done … it was that window of time that was the most disturbing time for me in my creative work.”

Derrickson said he saw “weird inexplicable phenomenon” in some of the videos, but that he was truly moved by the human suffering he observed. He said that after showing some of the footage to actor Eric Bana, who plays Sarchie in the film, Bana was so disturbed he couldn’t sleep.

As for the impact on his own life, while he said directing “Deliver Us From Evil” deepened his Christian faith, Derrickson noted that he went into the process with a skeptic’s mentality.

“When I went into the whole process of researching all of this and looking at all of this I made a conscious choice not to be thinking about it philosophically or theologically, but to look at it a bit more skeptically,” he said. “What does this really look like? How credible does this seem? And I was genuinely surprised at the power of the testimonials of the videos and the documentation of credible cases.”

While he believes that the majority of things that are blamed on the devil or demonic forces are “nonsense,” Derrickson said it’s tough to dismiss all claims of possession and infestation.

“I think you have to be unreasonable or have a dogma against anything supernatural to dismiss all of it outright,” he said. “It certainly had a deepening effect on me in my recognition of these dark mysteries of the world.”

Derrickson said he believes that something mysterious and “spiritually significant” seems to be going on in legitimate cases, arguing that open-minded people can’t dismiss what they’re seeing as mere mental illness.

He told TheBlaze he’s hoping to show viewers that “the world is more than just a material world.”

“Deliver Us From Evil” is loosely based on a true story, but also mixes in its fair share of fictional tidbits; it relies heavily on experiences Sarchie documented in his memoir, “Beware the Night.”

“I wanted to make sure I got the real guy, who he is, who he was as a cop … and I wanted to really portray his movement from skepticism from faith,” he said of Sarchie’s character. “What I did was I built sequences around that and characters around those aspects of the book.”

Here’s a clip of Sarchie discussing possession and the film based on his experience below: