(NewsNation) — A classmate who knew the alleged Idaho killer said Bryan Kohberger’s behavior changed noticeably in the days after the deaths of the four college students.

In an exclusive, 22-minute interview with NewsNation, graduate student Benjamin Roberts said he remembered Kohberger as typically being stressed and exhausted.

“I did notice he was showing up to class a little late sometimes, he always had a coffee in hand, he always seemed to be just perpetually exhausted,” said Roberts, who was also a graduate student studying criminal justice at Washington State University.

“Bryan seemed like he was on the knife’s edge between exhaustion and worn out and at the time it was extremely difficult to tell which was which,” Roberts said.

However, after the deaths of Kaylee Goncalves, Madison Mogen, Xana Kernodle and Ethan Chapin, Roberts said Kohberger became chattier and more social.

“He did seem to get a little chattier going into the later parts of the term,” Roberts said.

The full interview with Roberts will air tonight on NewsNation Prime at 6 p.m. Central/7 p.m. Eastern. Find NewsNation on your cable or satellite provider by using our Channel Finder.

Roberts said the kind of stress and exhaustion he typically saw in Kohberger can be typical for grad students. It didn’t raise any red flags because he said Kohberger didn’t appear to be falling apart in other ways.

The WSU campus in Pullman, Washington is just a 15-minute drive from Moscow, Idaho and Roberts said he and others made the short drive between the communities for many reasons. Authorities seized a computer and other evidence from Kohberger’s apartment on Friday after his arrest.

Overall, Roberts described Kohberger as awkward. He said he was the kind of person who wanted to make sure everyone knew he was the smartest person in the room.

“He had to make absolutely sure you knew he was smart, he had this intellectual capacity,” Roberts said.

Roberts doesn’t recall Kohberger talking specifically about the Idaho case.

Roberts said he pulled back from Kohberger then, too busy with his own workload for more socializing. He said it’s been unnerving to have a crime like that committed so close to his school and to have someone he was in class with be the alleged killer.

“There’s something heavy about that,” he said.