Seventeen months to the day before he was stabbed to death in his USC lab, Professor Bosco Tjan, along with campus police and university administrators, was warned that his attacker wanted to kill him, documents obtained by Annenberg Media show.

David Jonathan Brown, a doctoral student in Tjan's lab, told the threat to a therapist at a Pasadena mental health hospital. As required by California law, the therapist alerted Tjan and the university on July 2, 2015, that "David Brown made a serious threat against your life," a copy of the written warning states.

A months-long Annenberg Media investigation, based on court records and more than a dozen interviews, reveals details about how Tjan and the university responded to this letter and possible warning signs, including a "long history of threats" described by the Los Angeles Police Department.

Tjan, 50, a beloved professor of psychology and the co-director of the Cognitive Neuroimaging Center, remained supportive of Brown, despite the warning and serious concerns the university's threat assessment team had about Brown, a former member of the team said. Brown took a semester-long leave of absence, but returned as a student in spring 2016, an LAPD detective on the case said.

A day before the Dec. 2, 2016, stabbing, Brown sat with Tjan at a conference table to hear a student defend a doctoral dissertation, a colleague said. The next day, Brown attacked Tjan outside his 10th-floor lab in the Seeley G. Mudd Building, a confrontation overheard by Tjan's department chair, Professor JoAnn Farver, from her office down the hall.

She saw Brown standing over Tjan's body and heard him yell, "You have been torturing me for years. I have finally had enough," according to an LAPD search warrant affidavit.

Campus police found Brown a few minutes later in a nearby stairwell. The 28-year-old was charged with first-degree murder three days after the stabbing and remained in jail for the next 15 months. In January, he was found not guilty by reason of insanity. Last month, a Los Angeles County Superior Court judge committed Brown to Patton State Hospital, where he could spend the rest of his life.

A key question in the aftermath of the killing: Under what circumstances was Brown allowed to return to campus after he threatened the life of Tjan?

"There wasn't really a system in place to make sure [Brown] was really all right to come back," said Sgt. Josh Voyda of USC's Department of Public Safety, who was among the officers who responded to the scene of the stabbing. He is now the department's representative on the threat assessment team.

In a statement to Annenberg Media, a USC spokesperson said the university "took considerable action to ensure the safety of Professor Tjan, including extra patrols around Tjan's lab, restricting Brown's access to campus and alerting DPS officers."

The statement said that Tjan advocated for Brown's return to the lab and that there were no incidents between his return and the deadly attack. The statement said the university "persuaded Brown to take a leave of absence" after the written warning from his doctor, but did not identify who made the final decision to allow him to return to school.

In the months after the killing, USC reorganized its threat assessment team, including creating an Office of Campus Wellness and Crisis Intervention and hiring a chief threat assessment officer. DPS Deputy Chief David Carlisle, the department's spokesman, said the team has put in place a new system to track threats so that cases "don't fall through the cracks."

Warning signs
In December 2014, a doctoral student who shared lab space with Brown noticed a "change in Brown's behavior" and said Brown began to "correspond with her via email about manic episodes," according to a search warrant affidavit.

It's not known whether the student reported this behavior at the time. Warning signs, however, continued.

On June 25, 2015, Brown caused a disturbance in Tjan's lab that led to a DPS report, Carlisle said. The report said that a student "intentionally damaged University property inside a lab" and that the university's Student Affairs and Judicial Affairs offices were notified.

A week later, on July 2, 2015, the written warning arrived from Las Encinas Aurora Behavioral Health Care, a mental health hospital in Pasadena.

It was addressed to Bosco Tjan and read in part, "As required by law, we must notify any person whose life has been threatened by a patient. … This is to advise you that our psychiatric evaluation team (PET) member became aware that David Brown made a serious threat against your life."

The so-called Tarasoff warning, required by state law, is issued when a mental health professional believes a patient has made a serious threat of harm against someone.

"This is a mental health professional having to break their confidentiality," Voyda of DPS said. "That is absolutely a serious situation for that to occur."

The Tarasoff warning, a copy of which Annenberg Media reviewed, went on to say, "If you have any questions, please contact the USC Police Department."

Johnnie Adams, a former DPS officer who was on USC's threat assessment team at the time, said team members worked with Brown's family in Connecticut.

"We were able to get him to go back home and to get him medical treatment," Adams, who is now the campus police chief at Santa Monica College, said. In a statement, USC said it "persuaded Brown to take a leave of absence."

Brown took a leave the next semester, fall 2015, one of the LAPD detectives on the case, Maria Perez, said.

Adams said members of the threat assessment team "would've known about the threat." At the time, the team included representatives from Student Affairs, Student Counseling Services and the university's lawyers, he said.

The threat assessment team notified the LAPD, interviewed Brown's classmates and checked to see whether he owned any firearms, Adams said. They also spoke with Tjan.

"We told him all the concerns that we had," Adams said. "The professor told us he didn't think the threat was serious."

Return to USC
Brown returned to USC in spring 2016 and resumed working in the lab as a graduate student and Tjan's teaching assistant, according to the LAPD. In May 2016, an abstract Brown and Tjan co-authored was included in a Vision Sciences Society conference. That September, it was published in the Journal of Vision.

The day before Brown stabbed Tjan, a colleague saw the two of them around a conference table at a Ph.D. dissertation defense.

"David Brown was only one student away from Bosco," said Professor Irving Biederman, who was in the room at the time.

Carlisle of DPS said the decision to approve Brown's return was not made by campus police.

"It was up to [Tjan's] department who, I presume, in their best judgment decided that it wasn't a risk," he said. "But it obviously was."

Farver, the chair of the psychology department, which oversaw Tjan's lab, declined to comment when approached in her office last week.

Brown's public defender, Steve Schoenfield, said Tjan was Brown's biggest advocate, even after he learned of the threat against him.

"He still wanted David in the program and wasn't in fear of David," Schoenfield said. "Even people as smart as Dr. Tjan were unable to see it."

Said Voyda: "This is their field. They're studying brain chemistry and they probably thought they had a pretty good handle on what was going on, and unfortunately they really didn't see what was going on in David Brown's head."

"He didn't really come to anyone's attention that he was still having mental health issues, until the day he killed Professor Tjan," Voyda said.

Policy changes
Brown's lawyer said he wishes there had been more intervention in his client's case. "He really slipped through the cracks," Schoenfield said.

In the months after the stabbing, USC reorganized its threat assessment team and created an Office of Campus Wellness and Crisis Intervention. A memo from USC Provost Michael Quick in May 2017 said, "The tragic death of Professor Bosco Tjan in December reminds us that we have to constantly reassess our efforts in these areas."

"When somebody leaves and you know that they had mental health issues when they leave," Voyda said, "there's got to be something in place when they come back so that you can get an assessment as to where they are now."

As part of the reorganization, the university created the position of chief threat assessment officer and hired Patrick Prince, whom Quick described at the time as "a nationally recognized expert in workplace violence prevention."

"Often the left hand and the right hand don't talk to each other well," Prince said in an interview this week. "What we're trying to do, through my office, is make sure all of these [parts of the university] talk to each other
sooner."

Prince is a longtime member of the Trojan Family; he is an alumnus, along with his parents and his son. He was a reserve officer in the LAPD for 25 years and has worked as a threat assessment consultant on hundreds of cases. He said he wants to be visible around campus in his new role of keeping the community safe.

"If they see us and they feel us, then they know we actually know what we're talking about," Prince said. "I want to see their world, because ultimately our interventions are going to take place in their world."

"I just want to make sure everyone here goes home every day," he said. "I want students to come here and grow. I don't mind weird. I don't mind different. I don't accept threatening and dangerous."

"He thought Bosco was the ringleader"
Just after 4 p.m. on Dec. 2, 2016, Brown stabbed Tjan to death near the door of his lab in the Seeley G. Mudd Building.

When DPS found Brown in the stairwell, he had blood on his hands. When LAPD detectives searched his house near USC's campus the next morning, they found handwritten notes documenting Brown's "negative interactions with professors at USC," according to a search warrant.

In March, Brown, who is now 29 years old, was committed to Patton State Hospital in San Bernardino County after a judge ruled him not guilty by reason of insanity in Tjan's death. The prosecutor, public defender and judge all agreed that Brown was severely mentally ill at the time of the crime, based in part upon the assessments of two court-approved psychiatrists.

Brown's public defender said his client still suffers from mental illness.

"He thought a lot of the students at USC were hired actors–they weren't really students," Schoenfield said. "He thought the doctors in the neuropsych department, including Dr. Tjan, were all conspiring against him and were actually doing human experiments on not only him, but other students."

Schoenfield said Brown thought Tjan was the "ringleader" of the experiments.

"He had clearly believed that there were ongoing experiments that would shock him, make his body shake, make him hear things and ultimately kill him," Schoenfield said.

Patton State Hospital is a "locked-down facility" and Brown won't be allowed to leave unless a court rules that he has recovered, his lawyer said.

"They work with him and hopefully he'll get better and do better," Schoenfield said. "It's a one-day-at-a-time-type thing."

"A brilliant angel"
In the week after the killing, hundreds of people gathered at Tommy Trojan for a memorial celebrating Tjan's life and work. USC President C.L. Max Nikias called Tjan "a giant within the academy." His research focused on vision loss and perception, and he had received a grant to study how blindness changes the brain, the university said.

"Our sorrow and our anger are real," Nikias said. "Yet let us also be ever mindful of the enduring nature of his contributions to his field."

More than a year later, when her husband's killer was found not guilty by reason of insanity, Carissa Pang addressed the court.

"I feel helpless being thrown into a single-mom life because one man decided to end my husband's life," she said. "I feel helpless when my son asks me why his father was killed."

Tjan's son was 9 at the time of his father's killing.

"I feel helpless when my son asked me why the murderer did not see a doctor and take medicine to get better," Pang said. "My son lost a role model who knew how to fix nearly everything, but a mother does not have good answers."

"Our lives are diminished by his absence," Tjan's longtime colleague Biederman said. "He was brilliant. … He was the sweetest, nicest guy you could have. … And he was extraordinarily generous."

Biederman described Tjan as a "brilliant methodologist" who helped pioneer the design and operation of the neuroimaging lab. The first day the lab was open, Tjan taught the first class, he said.

"He knew just an extraordinary array of things in areas you were amazed that he could be that competent in, that knowledgeable about," Biederman said. "So students or colleagues would come to him often with quite challenging problems, and he would stop what he was doing and give you the benefit of his fabulous skills and intelligence in helping you.

"Everything he touched he made better," Biederman said. "Anyone who knew Bosco would say you can't hate Bosco. He's an angel–how could you hate him?"

If you or someone you know is suffering from mental illness, help is available. Contact USC's counseling services at 213-740-7711 or LA County's mental health crisis line at 1-800-854-7771. If you feel your safety or someone else's safety is being threatened, contact the DPS emergency line at 213-740-4321 or 911.