The University of California, Davis, chancellor has defended herself over criticism surrounding the campus police force's pepper spraying of peaceful demonstrators as information emerged about the officer at the heart of the incident.

Video footage of Lieutenant John Pike and another officer in riot gear casually spraying an orange cloud at the heads of protesters who were sitting peacefully on the ground has sparked national outrage since it began circulating online Friday night.

Students gathered on campus on Tuesday for the second time in as many days to condemn the violence and urged university officials to require police to attend sensitivity training.

The UC Davis chancellor, Linda Katehi, who has faced criticism from students over Friday's incident, defended herself during a town hall meeting on Tuesday night. She told an auditorium filled with more than 1,000 students that she asked police to remove tents from the university's quad but did not direct them to forcibly remove the demonstrators.

"I explicitly directed the chief of police that violence should be avoided at all costs," she said. "It was the absolute last thing I ever wanted to happen."

She stressed that students have a right to demonstrate peacefully.

"Because encampments have long been prohibited by UC policy, I directed police only to take down the tents," she said. "My instructions were for no arrests and no police force."

Pike, another officer and the campus police chief have been placed on paid administrative leave following the incident, which has generated international attention for the 32,000-student campus, west of the state capital.

Not all the students at the meeting were satisfied with the response from Katehi, who attended a rally on campus on Monday and apologised to students. Puneet Kamal, 22, an environmental science and policy major, was among those lined up to ask questions on Tuesday.

"She didn't say 'I'm sorry that I did this, or I'm sorry I made this call,'" Kamal said. "She said 'I'm sorry that this situation had to happen.' Where's the blame going to?"

Pike is a retired marine sergeant who has been honoured for his police work on campus, but he also figured in a discrimination lawsuit against the university.

He has twice been honoured by the university for exceptional police work, including a 2006 incident in which he tackled a scissor-wielding hospital patient who was threatening fellow officers. Afterwards, he said he decided against using pepper spray because it might harm his colleagues or other hospital patients.

As the controversy over the spraying incident has grown, images of the lieutenant have become the subject of a popular blog, which features his image superimposed on famous paintings and spraying famous figures, from Gandhi to John F Kennedy.

Dieter Dammeier, an lawyer for the Federated University Police Officers Association, the union that represents UC Davis officers, said the operations plan issued by the department includes the use of pepper spray. Dammeier said he does not represent Pike because he is a manager.

"The officers were doing simply what they were instructed to do by upper management there," Dammeier said, referring to police, not university, management.

On Tuesday, state lawmakers announced they would hold a hearing on the pepper-spraying incident. Assembly speaker John Perez sent a letter to the University of California Board of Regents chairwoman, Sherry Lansing, and the UC president, Mark Yudof,asking for a system-wide investigation.

"Students, parents and the public deserve to have answers to the myriad of troubling questions these incidents have raised," Perez said in a statement.

Yudof later announced he had appointed former Los Angeles police chief William Bratton to review the UC Davis incident and provide "an independent, unvarnished report about what happened."

Student government leaders on campus condemned the use of pepper spray on student protesters and called for Katehi to resign if she fails to enact reforms.

The student government passed a resolution on Monday night calling on the state attorney general's office to investigate campus police misconduct. The students are demanding police go through sensitivity training, seek more student representation and review policies on student protests.

Katehi has already asked the county district attorney's office to investigate, and the chief deputy district attorney, Jonathan Raven, confirmed on Tuesday that the department will look into the matter.

The attorney general, Kamala Harris, was deeply disturbed by the videos of the incident, spokeswoman Lynda Gledhill.

On Tuesday, about 50 tents formed an encampment on the site where the pepper-spraying happened as students went about going to class. Katehi showed up unexpectedly and asked to address students and occupiers during their general assembly meeting. She left after waiting about 30 minutes for her chance to speak.