Bryan Kohberger’s childhood friends claim he was a bully and used heroin in high school

Mr Kohberger has been extradited back to Idaho to face charges

Former high school classmates of the man accused of murdering four students at the University of Idaho have alleged that suspected killer Brian Kohberger was bullied before becoming a bully himself and allegedly using heroin.

The former classmates made the comments on an upcoming episode of 48 Hours titled “The Idaho Student Murders” set to premiere Saturday on Paramount+.

One former classmate knew Mr Kohberger in college at Washington State University, and recalled him being opinionated but otherwise "comfortable around other people,” according to a CBS News report about the episode.

"He was very quick to offer his opinion and thoughts," Mr Roberts said. "He would describe things in the most complicated, perhaps academic way possible."

48 Hours correspondent Peter Van Sant then asked Mr Roberts if he thought Mr Kohberger was "trying to impress people."

"It was like he was trying to convince people that he knew what he was talking about," Mr Roberts replied, per CBS.

According to the former high school classmates who spoke to 48 Hours, Mr Kohberger was overweight and was bullied until his senior year when he lost 100 pounds.

Casey Arntz, one of the former classmates, said he became "rail thin," and that "after that weight loss … a lot of people noticed a huge switch."

"When Bryan would get kinda angry with [her brother], he would gaslight him and get physically aggressive,” she said, adding that Mr Kohberger would put her brother in chokeholds.

Another classmate, whose name is Bree and asked to have her last name withheld, said Mr Kohberger allegedly began using heroin.

"You just saw him becoming more self-destructive. He really stayed secluded,” she said, adding that after graduating he began trying to get sober.

Bree continued: "He was telling me that he wanted to get sober, that he was getting sober. And he wanted to let me know ‘I’m gonna do better I’m gonna be better.’"

He began studying criminology in college, and attended a wedding in 2017 where he and Ms Arntz saw each other for the last time.

"I gave him a hug and I said ‘you look so good, I’m so proud of you,’" she said.

Bree said that his "goal was just to change the world for the good around him" during his time in college.

"He wanted to do something that impacted people in a good way," she told 48 Hours. "People were not his strong suit, and I think through his criminology studies, he was really trying to understand humans and trying and understand himself."

Bree went on to say she doesn’t understand what happened to bring him to a place where he is the suspect in a quadruple murder.

"Where did it go wrong?" she asks in the show. "What happened … why didn’t I see it?"

Mr Kohberger has since been extradited back to Moscow, Idaho, to face murder charges. He has not yet entered a plea in the case.

“This is out of character for Bryan, these allegations,” Monroe County public defender Jason LaBar said during Mr Kohberger’s extradition hearing, per Today. “The family wants the public to know that Bryan is a caring son and brother, that’s he’s responsible, that he is devoted to them.”