LOS ANGELES -- Police have identified the student they believe was responsible for stabbing a professor to death at the University of Southern California.

Los Angeles police say 28-year-old David Jonathan Brown of Los Angeles was booked on a charge of murder in the death of Bosco Tjan, a psychology professor and neuroscientist. Brown, who was arrested shortly after the stabbing, was being held on $1 million bail.

Though details of the motive weren’t released, Los Angeles Police Officer Meghan Aguilar said Tjan was specifically targeted and that the attack wasn’t random.

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A David Brown is listed as a graduate student in psychology on USC’s website. Tjan oversaw graduate students in the department and was killed in the building that houses the lab he ran.

Aguilar said Tjan was killed inside the Seeley G. Mudd building in the heart of campus. Aguilar could not say who called police but said it wasn’t the professor or the student.

The victim’s age was originally reported as 25. Later, police said they could not immediately confirm the man’s age, CBS Los Angeles reports. Public records list Tjan’s age as 50.

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, USC President C. L. Max Nikias said in a letter addressed to the USC community.

“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 in a statement that investigators believe the attack “was the result of a personal dispute.”

Chris Purington, project manager at Tjan’s lab, said he never heard of anyone having a problem with Tjan - a married father of one son - and had no idea who would have wanted him dead.

“He was somebody who really cared about people. I know he cared about me,” 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.

Purington traveled with Tjan for various science conferences and said that everyone knew and loved the professor.

“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,” Purington said. “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 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 to death 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 percent of the more than 54,000 people who applied for its freshman class this year.