Idaho student killer Bryan Kohberger got his first hands-on experience as a burglar while pilfering homes to fund a teenage heroin addiction, according to a new book.

“He was a heroin addict as a young guy [in Pennsylvania], and he was breaking and entering into houses,” crime novelist James Patterson told Lawrence Jones on “FOX & Friends” Wednesday morning. “He’d been doing it for years, and that’s exactly what happened in Moscow. He broke into this house and killed these four beautiful students.”

Patterson teamed up with investigative journalist Vicky Ward on “The Idaho Four: An American Tragedy,” which dropped earlier this week.

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While Kohberger has no publicly visible criminal record in his home state, he was forced out of a security job for reasons that have not been made public and reportedly has an expunged 2014 conviction for the theft and sale of his sister’s iPhone after a stint in rehab to pay for his heroin addiction when he was 19. In 2023, police confirmed to Fox News Digital the case had been expunged and said they had no record of it to share.

Kohberger’s dad, Michael Kohberger, told police that his son had just gotten out of rehab, swiped the phone and paid a pal $20 to drive him to the mall, where he allegedly sold it for $200, ABC News reported previously.

The killer, now 30, was going to face a capital murder trial next month until he unexpectedly changed his plea on July 1, when he admitted to four counts of first-degree murder and one of felony burglary. He acknowledged that he pre-planned the slayings and that when he entered the off-campus rental home at 1122 King Road, he intended to kill.

The authors found victims from Kohberger’s past in Pennsylvania, where he spent most of his life, who shed new light on his capacity for manipulation and plotting.

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“I felt chills when Connie Saba told me the story of how a teenage Kohberger had manipulated her into inadvertently telling him when she’d be out of the house to visit her son, Jeremy in jail, because he planned to break into her house and steal an iPad and other things from her,” Ward told Fox News Digital.

It was a striking betrayal, she said, because Kohberger had next to no friends and Jeremy Saba might have been the only one.

“Connie Saba had been nothing but welcoming and kind to him, so it was a devastating breach of trust – and when Connie Saba imitated Kohberger coming back a year or so later to apologize to her for the break-in (as part of his rehab process), she showed me the creepy way he just ‘appeared’ in her kitchen like a ghost, frightening her,” she said. “One could imagine him just ‘appearing’ at 1122 King Road on the night of the murders.”

READ BRYAN KOHBERGER’S SIGNED KILLER CONFESSION

Kohberger cased out the rental home around a dozen times before the murders, according to court documents. Before school officials had it razed last year, it was situated on a slope in front of a parking lot, giving Kohberger a potential vantage point overlooking multiple windows, including those of 21-year-old victim Madison Mogen’s bedroom.

“Mark Baylis, a former Navy SEAL, believes Kohberger successfully stalked him and his property for hours, days possibly, to steal valuables from him,” Ward added.  “It showed the cold-blooded, calculated side of Kohberger – a side that I think we all saw in court in early July when he pled guilty – with zero emotion.”

Kohberger stood up in court, with his back straight, admitting to the murders without a glance at his parents or those of the victims, most of whom were in the room. In the gallery near the defense table, his father wiped away tears and asked a bailiff for water. At one point, even Latah County Prosecuting Attorney Bill Thompson choked down a tear as he wrapped up a summary of the prosecution’s case.

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Throughout the proceeding, Kohberger fixed his eyes on lawyers in the room, the judge, and occasionally leaned over into the ear of his lead defense attorney, Anne Taylor.

The 30-year-old was a criminology student at Washington State University, a 10-mile drive from the crime scene.

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He’d barely been there for one semester but was already worried about losing his scholarship, Patterson revealed.

Kohberger had no meaningful connection to the victims, 21-year-olds Mogen and Kaylee Goncalves, and 20-year-olds Xana Kernodle and Ethan Chapin. But Patterson believes Mogen was the primary target when he snuck into the off-campus home at 1122 King Road on Nov. 13, 2022.

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She and Kernodle both worked at the now-shuttered Mad Greek restaurant, which had vegan menu options that the author believes appealed to Kohberger’s meat-free diet.

“He obviously had a big problem with women,” Patterson said, based on roughly 300 interviews he conducted and public documents. “We believe he was targeting Maddie and things had happened… He was going to lose his scholarship.”

Kohberger was pursuing a Ph.D. in criminology at Washington State University – where he reportedly butted heads with other students. After his arrest, the school said it had cut ties.

Kohberger’s defense did not respond to a request for comment.