LOS ANGELES (CNN) -- A group of protesters in Los Angeles did exactly what critics of George Zimmerman's acquittal didn't want -- they vented their anger through violence.
Police said the group damaged cars and businesses along Crenshaw Boulevard, a major thoroughfare. Officers made 13 arrests.
Now, police say they've had enough.
Starting Tuesday, LAPD will have a "much stricter posture" in the way it handles protesters in the area. Police Chief Charlie Beck said anyone blocking streets without a permit could go to jail.
"Unfortunately, the rights of the many have been abused by the actions of a few," Beck said late Monday night.
Three days of protests
Police emphasized that the vast majority of protesters in Los Angeles -- and around the country -- have rallied peacefully since Saturday, when Zimmerman was acquitted of charges in the death of 17-year-old Trayvon Martin.
But some Los Angeles protesters hurled rocks, batteries and chunks of concrete toward police over the weekend. Officers responded by shooting bean bags.
And on Monday night, a protester struck a news photographer in the head with a hard object. The impact knocked the camera out of the hands of the photographer, who works for CNN affiliate KCAL.
Memories of 1992
Los Angeles County Supervisor Mark Ridley-Thomas cautioned against demonstrations spiraling into deeper violence, stirring memories of city's 1992 riots that left more than 50 people dead.
Those riots were spurred by the acquittal of several LAPD officers who were videotaped beating Rodney King nearly to death.
"Twenty-one years ago, we witnessed what can happen when there's a reaction to a verdict," Ridley-Thomas said. "Non-violence ... is the most effective way to communicate how to address injustice."
Violence in Oakland
Los Angeles isn't the only city grappling with violence after the verdict.
Nine people were arrested in Oakland, California, during protests that ended around midnight, Oakland Police Officer Johnna Watson said early Tuesday morning.
Some protesters threw rocks, bottles and firecrackers at police, Watson said.
Just a sideshow
Civil rights leader John Mack praised the "overwhelming" number of protesters in Los Angeles who demonstrated peacefully. He said the fringe hooligans behind the violence "have their own agendas that have nothing to do with justice, and very little to do with Trayvon Martin."
Los Angeles Mayor Eric Garcetti agreed.
"Violence here is something that ... takes the wishes of the Martin family, that asked for non-violence, and disregards it," Garcetti said.
"If you truly care about the Martin family, if you truly care about the underlying issues, the last thing you should be doing is taking to the street, stealing scooters out of people's hands, assaulting people, smashing windows."
Many critics of Zimmerman''s acquittal are protesting not on the streets, but online.
More than 350,000 people have signed a MoveOn.org petition started by the NAACP asking for the Justice Department to file civil rights charges against Zimmerman.
Two petitions to the White House seeking such charges had more than 18,000 signatures between them.
Taking Zimmerman's side
Meanwhile, Zimmerman's parents, Robert and Gladys Zimmerman, defended their son in an interview with ABC News.
The parents said they are sorry for what happened, but insisted their son is not a racist.
"Absolutely not. He's never been taught to be a racist," Robert Zimmerman said.
He added that the family has received an "enormous amount of death threats."
Gladys Zimmerman said she would pray for Martin and for those now demanding vengeance after the verdict.
When asked what she would say to Martin's parents, she said: "We are deeply sorry for this tragedy."
While few -- if any -- Zimmerman supporters held rallies celebrating the verdict, the "George Zimmerman is Innocent" Facebook page had garnered about 25,000 "likes" by Tuesday morning.
Some suggested Zimmerman was racially profiled.
"If Zimmerman was black, would people act the way they they're acting now?" Ben Biller posted on the page.
CNN's Tina Burnside, Dottie Evans, Dave Alsup and Michael Pearson contributed to this report.
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