It was five days after Christmas in 1989 that Collier Landry heard what he said sounded like “a body hitting a wall.”

It was late at night, and the 11-year-old was in bed, not knowing that his mother, Noreen Boyle, was being murdered in their Ohio home.

“I will never forget those sounds – they haunt me,” the now-46-year-old told Fox News Digital. “But there was nothing I could have done to prevent what may have been occurring.”

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“I was a little boy,” he shared. “I was asthmatic. My father was big and scary, and I was still trying to figure it out. But then when I heard my father’s footsteps down the hall, and I could see his shoes out of my peripheral vision in the doorway, I knew something had happened.”

Landry said he suddenly heard a voice “screaming inside of me.” It warned him not to look up. He pretended to be asleep.

“I am convinced to this day that if I had chosen to look up, I would not be sitting here right now,” said Landry.

The case that would become a local media circus is being explored on Oxygen’s true-crime series, “A Plan to Kill.” It examines the true tales of disturbed killers who spend weeks, months or even years plotting the demise of their victims. 

Landry, who has launched a podcast, said it was important for him to detail how violent crimes impact the children of perpetrators.

“I think stories like these are really important to hear, to know that somebody can work for justice, to know that law enforcement will eventually listen to you, that you can get justice,” Landry explained.

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Landry described Boyle as a loving and doting mother.

“So many of my childhood friends have fond memories of her,” he beamed. “She was so kind, so supportive of people. I remember every holiday season; I would have to donate half of my toys to Toys for Tots, because she wanted me to learn the value of giving. She also wanted me to realize how fortunate I was as a child to have a mommy and daddy, to have a roof over my head, to have toys in my toy chest.”

“I wasn’t allowed to just pick out the random toys that I didn’t like,” he chuckled. “I had to sacrifice some of the ones I did like, because my mother wanted me to sacrifice for the good of others and to have compassion. That has stayed with me my entire life since.”

Landry’s father, Dr. John Boyle, was a prominent osteopath. But life at home was far from blissful.

The Boyles had lived in Mansfield since 1983, having moved from Virginia, where John had worked at a Navy clinic. During the marriage, John reportedly carried on many affairs.

Boyle filed for divorce in November 1989 after 22 years of marriage, charging extreme mental cruelty and gross neglect. During the divorce proceedings, John purchased a new home in Pennsylvania, court documents revealed. He began to relocate his medical practice to Erie from Mansfield.

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Landry described how he and his mother were “fearful” of the patriarch, who “was a very violent guy.”

“Towards the end, my mother was downtrodden because of my father,” Landry explained. “He was becoming more and more aggressive towards me, saying horrible things. Like, ‘I’ve started a new family, I’m going to make sure you are both living on the street.’”

“I think it all started to weigh in on my mother,” Landry reflected. “At the same time, my mother was still full of optimism that she was going to make it through. And she did her best not to let things affect me… She did her best to be as strong as she could for me, and I for her.”

“She was optimistic that in the end, we would be OK,” he shared.

In the morning, after hearing the “scary sounds,” Landry ran over to his mother’s bedroom. She was gone. 

He then confronted his father, who insisted that “mommy took a little vacation” and there was no need to call the police.

“I knew right then that he had done something to her,” said Landry. “He told me this whole story about how she had gotten up in the middle of the night. I asked him about the thuds. He said that was my mother’s purse that she had thrown at him, and it hit a wall.”

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“He was gaslighting me,” said Landry. “I needed to find out what happened.”

Landry snuck away and called Shelly Bowden, his mother’s best friend. When officers came to the home, Landry insisted that his mother would never leave him. He told police he had heard his parents argue, followed by a scream and a loud thump.

“They didn’t believe me,” he said. “It wasn’t until [Captain] Dave Messmore came on the scene. He took me seriously. That’s how we launched this whole investigation.”

“I knew I was risking my life,” he shared. “I knew that my father was dangerous, that he was violent, but I didn’t care. I was going to find out what happened to my mother. All I cared about was finding my mother.”

Authorities obtained search warrants partially based on Landry’s word.

On Jan. 25, 1990, less than a month after Boyle went missing, police discovered her body in John’s new Erie home, the Mansfield News Journal reported. 

She was wrapped in a tarp with a plastic bag covering her head and buried two feet below the basement in “soft, white clay,” the outlet reported. A green carpet covered the floor.

At age 12, Landry became a key witness in his father’s trial. He took the witness stand, stared down his father and helped secure a conviction.

“I knew that if I did not testify against my father, and he somehow walked free, I would regret that for the rest of my life,” Landry explained. “If I had to go back and live with him because, of course, he would maintain custody as my father, he could have tortured me for the rest of my life.”

“He haunted me in a lot of ways, but it really would’ve been bad had he been acquitted,” Landry continued. “I needed to do what was right for my mother.”

A mistress, Sherri Lee Campbell, gave birth to a daughter in January 1990, less than two weeks after Boyle disappeared.

John maintained his innocence. He took the stand on his behalf, testifying for nine hours over two days. Former Richland County Prosecutor James Mayer Jr. called him “probably the biggest liar I’ve ever seen.”

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John was convicted of killing Boyle. He was sentenced to 20 years to life in prison for aggravated murder and 18 months for abuse of a corpse.

Landry found himself alone. According to the episode, his mother’s family refused to take him in, because he resembled John. His father’s family also refused to welcome him, because, according to Landry, they wanted him to recant his testimony.

“When your family abandons you at the lowest point of your young life, that affects you,” he said. “Even though I was adopted by a loving family, and I was very grateful for that when I was 13, you still feel like you’re walking the majority of your life alone. It’s very hard to reconcile.”

“But I do it every day,” he said quietly. “I put one foot in front of the other, smile and say, ‘Today’s another day.’”

Landry later moved to California to pursue a career as a cinematographer and director. He began using his middle name as his new surname.

Today, Landry is determined to turn his pain into purpose. He’s now a speaker and provides coaching to those who find themselves in similar circumstances.

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“My story is centered around a true crime story, but this is also a story of healing and resilience,” said Landry. “You can go through unimaginably tragic circumstances, come out on the other side and be OK.

“… That’s what I would tell my younger self – ‘You’re going to be OK. You’re going to make it.’”