"Exorcism is topic that draws an emotional reaction instantaneously," Thomas told 3TV's Scott Pasmore. "Everyone has an opinion on the topic and very few people know much about it."
Thomas, 53, told Pasmore that he himself has "performed exorcisms on six people a total of approximately 50 times."
He has seen about 100 people in the past four year who believed they were possessed by the devil, according to a piece in the Los Angeles Times.
Thomas' training and journey is chronicled in the book "The Rite: The Making of a Modern Exorcist," which was the basis for the Mikael Håfström-directed movie "The Rite." Thomas actually spent a week on set, serving as an adviser.
Journalist Matt Baglio wrote the book featuring Thomas and is part of the new docudrama. He said according to priests and exorcists, reports of possessions and demonic activity are on the rise.
"They are very clear that they are getting inundated with people who are coming to them and asking for help," he said in the film. According to the producers behind the new docudrama, their film "cuts through all the Hollywood hype about demonic possession, the devil, and the rite of exorcism and tells the true story about the ancient rite."
Religious leaders say there have been an increasing number of reports regarding possession.
Thomas shared some of his own experiences with Pasmore, explaining some of the signs of possession and how such a thing can come to happen.
"In cases where there is a demonic attachment or a demonic relationship, there are classic signs, and not all the signs appear in every single situation," he explained.
According to Thomas, those signs include an aversion to the sacred, an inability to go to church or pray, an inability to take Holy Communion, unexpected and unexplained physical strength, unusual knowledge, sudden proficiency in a foreign language and "taking on the appearance of something that would look reptilian."
"Those are signs I have personally observed and witnessed," he said. "I've seen them enough to where there's pause, but I'm not surprised like I used to be."
As for how it possession can happen, Thomas had a relatively simple answer.
"You have to invite a demon in or someone invites a demon in for you," he said.
Protection can be just as simple.
"For a person who may not be Catholic, it would be a prayer life, a moral life and a faith life," Thomas said. "For someone who may not necessarily be Christian, something along the same lines."
To learn more about "The Rite: The Making of a Modern Exorcist," or to buy tickets, visit TheRitePhoenix.com.