The attack occurred just past noon on the sixth floor of Young Hall, prompting swift police mobilization and leaving students shaken by the violence as word spread across campus.
One witness inside the lab told The Times that the alleged assailant, a 20-year-old male student in the class, walked up to the 20-year-old female victim and appeared to repeatedly punch her. The witness said he realized it was more serious when she slumped over, bleeding profusely from her neck.
It was also reported, Cyril Baida, a teaching assistant who was working in a lab across the hall, said he saw the victim stagger out of the lab while another teaching assistant applied pressure to her neck, Baida said.
"The poor girl was completely drenched with blood. She was talking at first but then she started fading away," he said. "We told her she was going to be fine and to keep breathing so she didn't pass out. I told the other TA that he was doing great so he didn't faint either."
News agencies also report, the victim underwent surgery for multiple stab wounds at Ronald Reagan UCLA Medical Center. Police say she is in stable condition.
Campus Police Assistant Chief Jeff Young says Los Angeles city police and campus police interviewed about 30 witnesses who were in or near the lab at the time of the attack.
Thompson is being held on $1 million bail.
The motive is under investigation, The Associated Press reports.
Russian President Vladimir Putin and German Chancellor Angela Merkel had had a few fights and used strong language because of the Ukrainian crisis in 2014