In 1990 Dr. John Boyle went on trial for the December 1989 murder of his wife, Noreen.

“I did not kill Noreen. I never harmed her at all,” Boyle testified, claiming that they’d had an argument and then she left their Mansfield, Ohio home on the night she disappeared.

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At his father’s trial, John and Noreen Boyle’s then 12-year-old son, Collier, testified that he heard a scream and two loud “thuds” on the night his mother went missing. The boy’s account helped to convict his father, who is currently serving a life sentence.

WATCH: Man Who Testified In Dad's Murder Trial At Age 12 Says, 'I Literally Stared Him Down The Whole Time'

“It wasn’t until after I had testified that my father went on a crusade for many years to try to get me to rescind my testimony,” claims Collier, now 40. He’s the subject of the documentary film, “A Murder in Mansfield,” in which he revisits his mother’s murder and confronts his father from inside Ohio’s Marion Correctional Institution.

Watch the video above to learn what Collier says he shared with authorities that helped lead them to Noreen's remains; and why he claims his mother’s murder was “completely premeditated.”

Tune in Wednesday to watch the rest of this Dr. Phil daytime exclusive. Check here to find your local listing.

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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Son Who Testified For The Prosecution In Dad's Murder Trial Says, 'There's A Little Part Of You That Doesn't Want It To Be True'