In 1990, 12-year old Collier testified for the prosecution in the murder trial of his father, Dr. John Boyle. He was found guilty of killing Collier’s mother, 44-year-old Noreen.

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Boyle, who is currently serving out a life sentence in Ohio’s Marion Correctional Institution, denied murdering Noreen for years. Collier says that even though he thinks his father is “a horrific human being,” he visited him in prison for years.

“There’s a little part of you that doesn’t want it to be true,” he says.

WATCH: Man Who Testified Against Dad In Mother's Murder Trial Claims, 'It Was Completely Premeditated'

When Collier confronts his father in the documentary film, “A Murder in Mansfield,” John finally admits he killed Noreen, but he claims it was an accident.

In an excerpt from the film, he says, “My intentions were not to kill her or do anything else to her, but then she picked up a knife,” he says to Collier, adding, “I pushed her, and she hit her head against that wooden table.”

How does Collier respond when Dr. Phil asks, “Did you get the sense that he expected you to buy this?”

Check here to find out where you can watch this exclusive daytime interview airing Wednesday.

Footage/photos provided by Investigation Discovery. “A Murder in Mansfield" premieres on Investigation Discovery and IDGO at 9 p.m. EST on Saturday, November 17, 2018.

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