OAKLAND -- Oakland Mayor Jean Quan shifted into damage control Thursday, asking hospitalized protester Scott Olsen and other Occupy Oakland demonstrators to cooperate with police investigating Olsen's head injury.

Quan visited Olsen, a former Marine and Iraq War veteran, on Thursday morning at Highland Hospital. She shook his hand, and apologized for what happened to him. She also encouraged him and fellow demonstrators to speak with police, a hospital spokesman said. Olsen was knocked down -- apparently by a tear-gas canister or other police projectile -- Tuesday night as authorities tried to keep protesters away from Frank H. Ogawa Plaza, in front of Oakland City Hall.

The protest group had been dislodged from their tents on the plaza by police earlier in the day.

Oakland police have promised a thorough investigation of the incident, which left Olsen with a brain injury that has impeded his speech. Alameda County prosecutors and federal investigators also planned to look into the violent clash.

The city has tried this week to recover from the confrontation, which attracted an avalanche of criticism from pundits, politicians and protesters. Television host Keith Olbermann called for Quan's resignation, and White House press secretary Jay Carney called on U.S. cities to preserve "a long and noble tradition in the United States of free expression and free speech."

Protesters started rebuilding their tent city Thursday, with at least a dozen tents erected on the plaza lawn by the evening. Quan had planned to speak to a large crowd that had gathered in front of City Hall on Thursday night, but she left without speaking because she would have had to wait in line, said her attorney, Dan Siegel.

Police kept a low profile as another crowd of at least 1,000 flocked to the plaza for the second straight evening.

But the heat kept rising for the Oakland Police Department on Thursday. Civil rights attorney Jim Chanin, who has fought the department on many reform issues, said the department on Tuesday had violated its own crowd-control rules, which call for medical services to be available when tear gas and other control measures are used.

Under court order, the department signed a policy requiring the safety precaution, stemming from a 2003 protest in which officers fired "less-than-lethal" munitions on a crowd at the Port of Oakland protesting the war in Iraq. The New York Times described it at the time as "the most violent (clash) between protesters and the authorities anywhere in the country since the start of the war."

Chanin said Tuesday's clash reminded him strongly of the 2003 incident. He said he doesn't yet know what the consequences to the department could be, though he noted that the department spent millions of dollars settling lawsuits in the wake of the 2003 dust-up.

Oakland's interim police chief, Howard Jordan, said Thursday investigators were still piecing together accounts from more than a dozen police departments that sent officers to Oakland to raid the encampment.

There are numerous videos of evidence to review, Jordan said, and it's not yet clear where Olsen was when he was injured.

Olsen's injury prompted vehement anger toward police during protesters' march around the city Wednesday night, but Jordan would not speculate whether the Daly City man had been hit by a police projectile such as a tear-gas canister, rubber bullet, wooden dowel or something else.

Though the veteran may have been injured by an officer from an agency other than OPD, Jordan said responsibility for the police response Tuesday night falls squarely on his own shoulders.

It's also not clear whether Tuesday's clash will further anger Judge Thelton Henderson, who has harshly criticized the Oakland Police Department for a nine-year effort to reform following a major corruption case. Henderson has threatened OPD with a federal takeover, and the department's reform efforts will be the subject of a hearing in his courtroom in January.

"I'm still looking into what happened," Chanin said, "but I'm looking at the response to Occupy Oakland and comparing it with all the other cities in the country, many of whom had many more people involved and just as challenging problems, and I ask why? Why are we always on national television as the example of the most egregious use of force?"

Siegel, who has advised Quan about how to deal with protesters, called Olsen's injury proof of police misconduct, and City Councilwoman Jane Brunner said the incident is Oakland's responsibility, no matter which police department hurt the former Marine.

At least one police department suggested officers may not be to blame for the incident.

"I haven't seen much, but given the nature of that individual's injuries, I'm wondering if he wasn't struck by something thrown by a demonstrator," said Chief Dennis Burns, of the Palo Alto Police Department.

The Oakland City Council will discuss Tuesday's police response at a special meeting Nov. 3 at City Hall, Councilwoman Rebecca Kaplan said in a written statement.

Occupiers on Thursday were expanding a shrine to Olsen built around the base of a memorial to military veterans. Vita McDonnell, 24, who was arrested in Tuesday morning's raid of the encampment, brought a box of candles and notebook in which she is asking people to write notes of encouragement to Olsen and reflections of events of the past several days.

"He was protesting our arrests," said McDonnell, a health-care assistant. "I felt very touched by it. This is really something I had to do."

Tuesday morning's police raid "felt like we were under attack. It was like a war zone," she said. After 13 hours in custody, mostly at the Santa Rita Jail in Dublin, she was released with a citation of unlawful assembly, she said.

Thursday's lull left more questions than answers about the future of Occupy Oakland, which has leapt to the forefront of the nationwide Occupy movement targeting banks, big business and a slate of other social and economic issues. The East Bay protests have captivated talk-show hosts such as Jon Stewart and Olbermann, and documentary filmmaker Michael Moore announced Thursday on Twitter that he would arrive at the Oakland site Friday.

The activism site MoveOn.org circulated a "Stop the police repression of Occupy Oakland" petition and Stewart contrasted the Oakland protest with more peaceful demonstrations around the country.

"What's going on, Oakland?" asked Stewart on Wednesday night's episode of "The Daily Show" after showing footage of tear gas being fired at protesters on Broadway. "Chill out."

Across the bay, Occupy San Francisco protesters remained in their encampment Thursday, a day after fears spread among the group that police planned to raid the camp.

San Francisco Mayor Ed Lee said in a news conference Thursday that he is seeing a better dialogue between the OccupySF camp and the city over concerns about public safety and public health. He stopped short of saying that the campers would be allowed to stay indefinitely, but said he supports a compromise that allows them to express their First Amendment rights as long as it does not impact public health.

Nobody wants what happened in Oakland Tuesday to happen in San Francisco, Lee added. He also said police had not intended to raid the camp Wednesday night despite the mobilization of hundreds of law-enforcement officers.

"The police had to get ready because of what they saw in Oakland," Lee said. "They thought there would be hundreds of people coming from Oakland to San Francisco ... and we didn't know what their intention was," Lee said. "We saw a lot of anger, a lot of frustration of individual people who wanted to come to San Francisco, and we didn't know what their ultimate intention was."

Staff writer Cecily Burt contributed to this story.