A student has stabbed a psychology professor to death on the University of Southern California campus in Los Angeles over a personal dispute.
Los Angeles police officer Meghan Aguilar said the professor, identified by university staff as Bosco Tjan, was killed inside the Seeley G Mudd building in the heart of the campus. A student was arrested.
Ms Aguilar said the student was being interviewed and that his name would be released after he was booked.
USC president Max Nikias identified Prof Tjan in a letter addressed to the USC community.
Prof Tjan joined USC in 2001, taught in the Dornsife College of Letters, Arts and Sciences, and served as co-director of the Dornsife Cognitive Neuroimaging Centre, Mr Nikias said.
"As the Trojan family mourns Professor Tjan's untimely passing, we will keep his family in our thoughts," Nikias said.
The USC Department of Public Safety said investigators believed the attack was not random and "was the result of a personal dispute".
Chris Purington, project manager at Prof Tjan's lab, said he never heard of anyone having a problem with the academic - a married father of one son listed in public records as 50 years old - and had no idea who would have wanted him dead.
"He was somebody who really cared about people. I know he cared about me," Mr Purington said through tears. "He mentored people and he looked out for them. He spent a lot of time thinking about what it means to be a mentor and guide people."
He said the professor gave him a job both after he graduated from USC and after graduate school at the University of California-Berkeley.
Mr Purington travelled with Prof Tjan for various science conferences and said everyone knew and loved him.
"People talk about scientists as very cold or robotic. Bosco is a guy that he could talk to anybody about anything," he said.
"He couldn't move through a room without being sidetracked in all these conversations.
"He just had this energy about him. Kinetic might be the word. He had a huge impact on my life."
USC was rocked last year by the beating death of graduate student Xinran Ji, who was attacked and beaten by several people as he walked back to his off-campus apartment late at night after attending a study session.
After Mr Ji's murder USC officials sought to reassure parents of Chinese exchange students that the campus and its surrounding areas are safe.
In 2012, Chinese graduate students Ming Qu and Ying Wu were shot dead as they sat in their BMW about a mile from campus.
USC has 44,000 students enrolled, including more than 10,000 international students. A highly competitive school, it enrolled only about 16% of the more-than 54,000 people who applied for its freshman class this year.