The paranormal investigator's new documentary tells the story of a house in Gary, Ind., that was reportedly "a portal to Hell"

Zak Bagans knows there will be skeptics.

The paranormal expert, who has been investigating hauntings on Travel Channel’s Ghost Adventures since 2008, just released a new feature-length documentary, Demon House, about a now-demolished dwelling in Gary, Indiana, that was said to be “a portal to Hell.” Bagans bought the home, sight unseen, after reading about then-residents Latoya Ammons and her family, who claimed to have experienced paranormal activity including physical contact, possession and levitation.

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“What attracted me to it in the first place was the reports of a little boy walking backwards up a wall,” Bagans, 40, tells PEOPLE. “A Child Protective Services caseworker, a psychiatrist and a nurse all witnessed it. Those things you just don’t hear too often.”

Bagans took a camera crew to Indiana to investigate and interview police officers and others who had come in contact with the house. “When I arrived, it was chaotic and I didn’t know what to expect or what I was going to find,” he says. “There was just a totally different vibe in and around that house. These eyewitnesses experienced incredible trauma.”

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The film, which also documents other severe conditions people experienced after being in the house—from a young girl’s suicide attempt to parapsychologist Dr. Barry Taff’s organ failure—concludes with Bagans, who also suffered damage to his own eyesight, boarding up the home’s windows and doors and locking himself inside for a night “to face it head on,” he says. “There were recurring moments of a growl and there were some noises that sounded like it was coming up the steps. That is permanently etched in my brain. To see darkness move in the house was unnerving.”

Yet confronting his fears is just a part of the job. “I get terrified,” he says. “Sometimes I don’t know how to deal with it, but we’re all tuned differently.” This experience “ranks as one of the most traumatic and yet fascinating cases that I’ve ever investigated,” he adds. “It’s one of those that I can’t ever get out of my head.”

As for non-believers, Bagans hopes the film will simply offer a different perspective. “It’s not my job to force people to believe things,” he says. “I respect and believe skeptics. This is my story and investigation. Just watch the journey. I’ll never forget what I went through. And if you want to believe in it, do. If you don’t, then you just never will. That’s fine. I focus my energy on what I believe in. And I believe in all of this.”