Nearly two weeks after a pro-Palestinian encampment at the University of California, Los Angeles, was attacked by counterprotesters, university officials still have not explained why security officers stood by for hours while the attack was underway, nor have they arrested any of those who swarmed in wielding metal rods, water bottles and firecrackers in one of the worst outbreaks of violence in the college protests that have rocked the country.

The extent of the policing failure has become clearer in recent days, as witnesses have come forward to describe a chaotic night of violence on April 30, in which students and bystanders repeatedly called 911 and nonemergency lines, finding little help and calls that were disconnected. A dispatcher told one caller pleading for help that they were ending the call because “I have actual emergencies to handle.”

One man was filmed by a local television station on the phone with emergency dispatchers, alerting them that people were getting hurt. “Security has abandoned this encampment,” he could be heard saying before lowering his phone and looking at it. “They just hung up on me again,” he said incredulously.

Miles away in Sacramento, staff members in Gov. Gavin Newsom’s office contacted the U.C.L.A. chancellor’s office shortly after 11 p.m. to make sure that law enforcement officers were responding to the scene, and were assured that more officers were coming, according to a person familiar with the situation, who described the discussions on condition of anonymity because they were not authorized to make them public.

But as the night wore on and there was still no intervention, the person said, the governor’s office moved to circumvent local authority and ordered California Highway Patrol officers to the campus. The state officers began assembling on campus at 1:45 a.m., a few moments before L.A.P.D. riot police arrived, but it took another hour to quell the clashes.