(NewsNation) — After the arrest of suspected Idaho college killer Bryan Kohberger, a lot of personal information about him has emerged on social media. A TikTok post from one user who says she knew him in middle and high school specifically grabbed a lot of attention.

As she scrubbed her memories in the TikTok video, Casey Arntz appeared to be stunned and shaken when speaking about Kohberger. During an interview with NewsNation host Chris Cuomo, Arntz said Kohberger, who is accused of fatally stabbing four University of Idaho students, was bullied during the formative years of his life.

“Personally, what I’m finding out from former friends and former classmates is that, you know, Bryan was bullied. When he was younger, he was an overweight kid. When I personally knew him, he was always good to me,” Arntz said.

Arntz believes the tables turned in high school and Kohberger may have taken on the role of a bully himself.

“Going into his senior year, he lost a lot of weight. It was then I hear that he might have become a bully. I was not there personally to see that. However, looking back at it, knowing how he knows my brother, knowing now how he knows my other friends, I wouldn’t put it past him because my brother has come out and said that he was bullying him when he was friends with him,” Arntz explained.

She said it seemed as if Kohberger always had to be the smartest person in the room, especially when her brother was around.

“It was like he was undermining him and just putting him down. My brother cut ties with him because of this, because they got too much of a torment for him,” Arntz said.

She does not recall any specific acts of violence from Kohberger but said she has heard he could become aggressive.

“He would get physically aggressive with people. He would get aggressive very quickly. I never saw it face to face, thankfully. And, again, going back to one of the things my brother said, when he would get kind of physically aggressive with him, he would kind of put you in a headlock and stuff like that. I never saw that,” Arntz said.

In speaking with her brother about Kohberger the past couple of days and considering the suspected killer’s background, Arntz said it seems like he’s trying to throw off law enforcement by staying nearly silent.

“He’s not talking because he knows how to work it. He knows the ins and outs of this. This is what he studied for years. So, to me, I don’t think it’s surprising that he’s not talking, because he thinks he knows what he’s doing. He’s trying to undermine law enforcement,” Arntz said.

In the interview, Arntz also remembered Kohberger’s alleged struggle with heroin addiction in high school.

“He did use me. I didn’t know at the time that he was using me to drive him to get heroin until probably a couple of days afterwards. It triggered me in a way, because I didn’t know that I could have been put in such a compromising position from him. But yeah, he definitely struggled with heroin addiction in high school,” Arntz said.

Arntz described the Kohbergers as a standard family in the Poconos, with Bryan Kohberger’s mother once working as a substitute teacher at Pleasant Valley and his father often sharing fun stories with Bryan’s friends.

“We had a lot of people coming in from New York, and we were used to all these people. But, they never stood out as anyone bad or good or crazy. They were just another family,” Arntz said, also adding: “His parents — again, I can speak on his mom and my brother can speak to both of them — are great.”

Kohberger has been arrested in connection to the Nov. 13 murders of Kaylee Goncalves, Madison Mogen, Xana Kernodle and Ethan Chapin in Moscow, Idaho.

Kohberger’s family released a statement through his public defender, issuing their support.

“First and foremost, we care deeply for the four families who have lost their precious children,” the statement read. “There are no words that can adequately express the sadness we feel, and we pray each day for them. We will continue to let the legal process unfold and as a family we will love and support our son and brother.”

Kohberger could be back in Idaho as soon as Tuesday after a hearing in Pennsylvania. He is not expected to fight extradition.