Idaho murder suspect Bryan Kohberger was an awkward “creep” who repelled girls in high school — and reportedly struggled with a heroin addiction in his late teens.

And those who knew the accused killer described him as an “outcast” whose transformation by his senior year of high school was so drastic — they thought he was a “new student.”

“I remember seeing him and thinking it was a new student. He was so heavy and he lost so much weight, he almost looked sickly or like it was an obsession. Around the same time, he became more aggressive and I think he became more of an outcast at that point. He became more withdrawn,” Dominique Clark, who attended elementary and high school with Kohberger, told The Post.

Kohberger, 28, was arrested in Albrightsville, Pa., Friday and charged in the Nov. 13 murders of four University of Idaho students who were stabbed to death as they slept — Kaylee Goncalves, 21; Madison Mogen, 21; Xana Kernodle, 20; and Ethan Chapin, 20.

Kohberger, who grew up in the Poconos, underwent the startling transformation before senior year at Pleasant Valley High School in Brodheadsville, losing maybe 80 pounds, Clark said. A fourth-grade yearbook photo of Kohberger shows a smiling, husky boy with spiky hair.

After his weight loss, he reportedly went from victim to aggressor, classmates said.

Kohberger was also a “heavy heroin user back in high school,” another former Pleasant Valley High School classmate claimed.

Casey Arntz shared the details of the accused killer’s checkered past in a series of videos posted on Friday.

In the video clips, Arntz shows photos of herself with Kohberger and other pals as well as screenshots of messages she had apparently exchanged with him. 

“I really didn’t have ‘Old Friend of a Murderer’ on my 2022 bingo list,” she said, still shaking and visibly distressed from learning the alleged mass murderer’s identity.

She showed a clip of her posing for a photo from 2017 with her friend Brandon, his wife, and Kohberger standing off to the right — facing the camera, but expressionless.

“Obviously that’s Bryan. Still had the dead face,” she remarked.

She said when she had spoken to him at the time, he told her that he was “clean” from drug use.

“It was nice to see him clean up,” she said, adding that he said he was working security detail at a school at the time.

“He seemed like he was better. Obviously that wasn’t true,” Arntz said. 

She shared another photo of her friend posing with Kohberger at a party at her friend’s house, noting that he “used to be a bigger kid,” compared to his skinny frame today.

The battle with drug addiction extended into college, a former classmate at Northampton Community College told Fox News.

The classmate, who did not want to be named, told the outlet that the two would talk “for hours” about his weight and drug battle.

Meanwhile, Clark described Kohberger as very bright, but odd — especially around girls.

“If he liked or was interested in a girl and she wasn’t, he didn’t understand why or just didn’t accept her saying no and move on and so he would have been labeled as a creep or something along those lines,” said Clark, now a critical care nurse who lives in Breinigsville, Pa.

“He hung out with the people who were outcasts together. He tried to hang out with people who were smart,” she continued. “He just didn’t really fit in with anybody.”

Another classmate, Sarah Healey, told Fox that Kohberger was bullied by high school girls, who would even throw things at him.

“It was bad,” Healey said. “There was definitely something off about him, like we couldn’t tell exactly what it was. 

Healey said that treatment might have been a motivating factor for Kohberger.

“I honestly think that’s what led up to this, because he didn’t get the proper help, and it was mainly females that bullied him,” Healey said.

Kohberger is being held in Monroe County, Pa., where his next court date is Jan. 3 in the Court of Common Pleas.

No motive for the savage crime has been revealed and any connection between Kohberger, a graduate student in the criminal justice department at nearby Washington State University in Pullman, and the Idaho students remains unclear.

In other developments:

“He was around the area at the time of the offense, I’m assuming they have his cell phone tracking data. That’s a pretty good assumption in today’s world,” LaBar said. “On the 12th or 13th [November], they certainly have him in or around Pullman or Moscow.”

LaBar said that he spoke with Kohberger Friday in an hour-long conversation, in which he appeared “calm and shocked about everything.”

“He’s a very intelligent man, I think everyone’s aware of that,” he said, adding that Kohberger “is aware of the situation and apparently he’s spoken to police also. I believe Idaho state troopers as well as Pennsylvania state police.”