A judge ruled Tuesday that a USC graduate student accused of stabbing a professor to death on campus was not guilty by reason of insanity.

The ruling, based on reports from two psychiatrists, means that David Jonathan Brown could spend the rest of his life in a state psychiatric hospital. The 29-year-old has a March 6 hearing to determine where he will be placed.

Brown killed his mentor, Siaufung "Bosco" Tjan, on Dec. 2, 2016, inside the University of Southern California building where the 50-year-old psychology professor ran an intensive lab that studied vision loss, authorities said.

The killing occurred on the final day of classes before final examinations. Prosecutors said that Brown told authorities he believed he was "a victim of human experimentation."

Tjan's widow spoke during the hearing in Los Angeles Superior Court.

"He was not a soldier in a war zone or policeman in a dangerous street. He was murdered in his research lab," Carissa Pang said, according to City News Service.

"I feel helpless when my son asked me why his father was killed," she said.

She said she told him that the killer was "having bad thoughts."

Brown's family "gives their condolences and hopes that you find some solace," defense attorney Steve Schoenfield told her.

Tjan's family will be notified of any changes in where Brown is housed and what treatment he receives, Judge Leslie A. Swain told Pang.

After the killing, Brown's fellow graduate students described him as nice and intelligent but possibly troubled.

Brenton Keller wrote on Facebook that classmates knew things weren't right because Brown wouldn't always finish his work and would go missing for weeks at a time.