A professor who was stabbed to death Friday afternoon in Los Angeles started his postgraduate academic career at the University of Minnesota, whose faculty he still worked with on research projects.

Bosco Tjan, 50, a psychology professor at the University of Southern California and a neuroscientist, was fatally stabbed Friday afternoon in what authorities say was a targeted attack by a student. Los Angeles police say David Jonathan Brown, 28, of Los Angeles, was booked on a murder charge and is being held on $1 million bail.

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 Center, according to university President Max Nikias. Tjan received his Ph.D. in computer science at the University of Minnesota in 1997, according to his LinkedIn page.

"As the Trojan family mourns Professor Tjan's untimely passing, we will keep his family in our thoughts," Nikias said.

At the U, Tjan cultivated his passion for human vision research while working with mentor Gordon Legge, a psychology professor with whom he collaborated until his death.

"He was an extremely generous and friendly student and colleague," Legge said Saturday. "Some of my past students have worked with him, and it's sort of become an academic family."

Legge said he last spoke with Tjan about a month ago and that Tjan visited the Twin Cities about once a year. Along with a team, they had been working on an ongoing project about visual accessibility in airports in partnership with the Federal Aviation Administration.

"Bosco is very insightful. He was coming at it with knowledge," Legge said. "He was a very active and important collaborator on this project."

Legge did not know the suspect's motives but said postgraduate programs can be incredibly stressful.

"You occasionally hear about these kinds of situations where a student reacts violently toward a mentor," Legge said. "Of course, you never expect it to come that close to home."

Tjan, who was married and a father of one child, is remembered by friends as intelligent, adventurous and passionate about social issues and affairs in Hong Kong. At the U, he was a member of the Hong Kong Student Association and found a band of friends who called themselves "Brothers Four," former classmate Lewis Leung said.

"We hung out quite a bit together, playing chess and hanging out in apartments," said Leung, of Minneapolis, a page designer at the Star Tribune. "We cooked together, went to the Boundary Waters, camping, hiking." Leung added: "I appreciate his ... dedication to making the world a better place."

Another colleague Susana Chung, who teaches at the University of California, Berkeley, met Tjan when she lived in Minnesota. Since they were both originally from Hong Kong, he helped her settle in as a newcomer, she said. They collaborated on many research projects, and Tjan was "brilliant, very fair and very ethical," Chung said.

Chris Purington, project manager at Tjan's lab, said he never heard of anyone having a problem with Tjan. "He was somebody who really cared about people. I know he cared about me," Purington told the Associated Press through tears.

He said the professor gave him a job both after he graduated from USC and after graduate school at the University of California, Berkeley.

"People talk about scientists as cold or robotic. Bosco ... could talk to anybody about anything," Purington 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."

The Associated Press contributed to this report.

Natalie Daher • 612-673-1775