LOS ANGELES (AP) — USC students were in disbelief Saturday over the stabbing death of Professor Bosco Tjan on campus Friday. Phd. student Shuyang Shi was in the Seeley G. Mud building at the time of the alleged murder.

“I feel really said. We were working in the lab and the police just told us to leave,” Shi said. “Everyone was just waiting outside the building and we didn’t know what happened.”

Los Angeles Police arrested David Jonathan Brown, of Los Angeles, shortly after the stabbing and booked him on a charge of murder in the death of Tjan, a psychology professor and neuroscientist. Brown, 28, was a graduate student who worked under Tjan. Police have not released a motive for the crime, but say they do not believe this was a random attack. Brown is being held on $1 million bail. It wasn’t clear if he has an attorney.

USC did sent text alerts out to students, but they didn’t provide many details about the incident.

“I was a little panicked when my friends back home started messaging me, student Grace Xu said.  “They said there was something violent and I was like ‘I have no idea what you’re talking about.’ ”

Tjan was an expert in the field of vision loss, teaching at USC since 2001 and serving as one of the directors of the cognitive neuroscience imaging center.

Former and current students are expressing their grief on social media saying things like:

His neighbors in Cerritos say they’d often see him with his wife and 9-year-old son. They’re also in shock to hear that he’s gone.

“That’s horrible,” Paul Richardo said. “To hear that something like that happened to one of my neighbors. That’s really sad.”