"One morning [my dad] picked me and this girl up at the Circle K on Monroe and said he would take me to school first then drop her off on his way back because he wanted to talk to my Mom. I never saw this girl again and a few days later it came out on the news that she had been killed," he wrote in a letter sent from an Idaho prison where he's serving time for an unrelated second-degree felony kidnapping conviction.
Ogden police announced in late September that a DNA match helped them crack the decades-old cold case and connect Gregory Seamons, who lived in Rebecca's neighborhood, to her rape and murder.
Rebecca's body was discovered in March 1983 by a pair of 11-year-old classmates who decided to arm themselves with BB guns and search for her after she disappeared. The duo found her body in a wooden shed near her elementary school, underneath an old mattress and wrapped in a blanket.
Police said her head had been smashed multiple times with a rock. Officers said they obtained semen swabs from Rebecca's body. Years later, those swabs were linked to Gregory Seamons.
He was then charged in 2nd District Court with murder and rape, both first-degree felonies. Prosecutors expect to extradite him back to Utah to face those charges.
But for now, Seamons remains in segregation at the Idaho prison due to the media attention his case has generated, he said in the letter.
"Lots of kids fool around sexually but that doesn't mean one kills the other. I am innocent of this charge and angry that they plan to blame it on a 15-year-old boy," Seamons wrote.
Ogden Major Crimes Sgt. Tim Scott said this is the first time Seamons has pointed the finger at his deceased father, a move he described as "convenient" considering the elder Seamons is dead.
"It's new information, definitely," Scott said. "Obviously we'll follow up any new leads."
But he said police are confident the right man has been charged with Rebecca's rape and murder.
Weber County Attorney Dee Smith said he would save any comment on the newest allegation for the courtroom.
Seamons wrote that he and Rebecca were friends and had started to meet and "fool around" about the time Rebecca was killed. Rebecca also was friends with one of his siblings, who even attended her funeral, Seamons wrote.
"She said she enjoyed spending time with me because she was sad at home," Seamons' letter said of Rebecca. "Her Dad was in poor health."
Rebecca's mother, Nola Mahon, who no longer lives in Utah, said she doesn't remember Seamons or his father and doesn't believe either one ever visited their home. But she said she is confident of the work performed by Ogden investigators.
"I think the DNA speaks for itself," she said. "Thank God for DNA."
Mahon said she was shocked by Seamons' allegations. She said her daughter never would have had consensual sex with him.
"She was a baby," she said. "She was just about to be baptized in the LDS church."
Mahon described Rebecca as sweet, loving and always a peacemaker. Her family adored her.
"She was an angel," Mahon said. "I know everyone says that about their children, but mine was. I would look at her at times and tell her, 'You're an angel and you were sent here by mistake to be my baby.' "
Seamons claims in the letter that shortly after Rebecca died, his father molested him in the shower, but he never told anyone until he was in his 30s. He said he suspects his father may have molested other youth.
Weber County court records from 1965 show that Larry Seamons was confined to a state mental hospital after he pleaded not guilty by reason of insanity to a charge of indecent assault on a 4-year-old girl when he was 21. Charging documents show he admitted he and the girl had been naked together in a bed.
Psychiatrists determined that Larry Seamons was "legally 'sane' and is of bright normal intelligence with a passive-aggressive personality with some paranoid traits," according to court records. He subsequently pleaded guilty to taking "indecent liberties" with the child, completed probation and as a result, the case was dismissed, court records show.
No other sex-related court charges against Larry Seamons exist in the Weber County court archives.
Gregory Seamons' mother couldn't be located for comment.
Seamons said he's not angry with Ogden police over the murder and rape charges because they're only doing their jobs.
"I should have told my Mom 30 years ago what I thought, and I probably wouldn't be in this situation," he wrote.
But he remains angry at his father for molesting him in the shower, according to the letter.
"... I'm also angry at myself because I should of told the Ogden police what I knew when I had the chance. At this point, I will wait until I have a lawyer who will help me. They might convict me of withholding evidence against my Dad, but not murder and at that, my evidence is only speculation."