Bryan Kohberger's WSU Classmate Says He Often Spoke Up, Except on Idaho Case

Bryan Kohberger was a chatterbox in class -- often speaking up to talk shop -- but he clammed up whenever the U. of Idaho murders were mentioned, so says one of his former peers.

Washington State University student Ben Roberts -- who was in the same graduate program with Kohberger last fall -- tells the Idaho Statesman the man prosecutors allege is a cold-blooded killer wasn't shy when it came discussing criminology theory ... that is, until 4 University of Idaho students were killed in November.

Roberts says he recalls Kohberger as incredibly engaged when it came to classroom discussions about their subject matter -- especially on forensic psychology (understanding a criminal's mindset). According to him, Kohberger would talk during every session of theirs.

However, Roberts also says he remembers Kohberger suspiciously going radio silent in the later fall months of the semester -- around the time the quadruple murder happened, which was brought up in at least 4 different classes he says they shared.

In all instances, it sounds like Kohberger didn't wanna chime in like he normally would ... something that gives Roberts, and an anonymous ex-classmate, pause now.

One other thing ... Roberts says he remembers Kohberger eager to debate and talk down to female students in his program, as opposed to being more measured and nonconfrontational with the guys. Aside from that, Roberts says he was pretty normal.

As we reported ... Kohberger has been charged with four counts of first-degree murder for the 4 Idaho deaths. He has yet to enter a plea, but his attorney has said he'll be exonerated.