LOS ANGELES (CNN) -- Unabated anger over the acquittal of George Zimmerman played out Tuesday in violent protests on gritty California streets and some other cities across the nation, as well as on social media sites.
In Los Angeles, where police were forced onto emergency footing by sometimes violent protests for the third night in a row, authorities said they would adopt a "much stricter posture" in handling the protests beginning Tuesday.
"Unfortunately, the rights of the many have been abused by the actions of a few," police Chief Charlie Beck said late Monday night after protests turned ugly.
Meanwhile, thousands of people turned to social media and online protests to voice their opinions, signing online petitions calling for civil rights charges against Zimmerman and posting pictures and essays discussing their dismay.
The Hispanic neighborhood watch volunteer had been accused of wrongly killing 17-year-old African-American Trayvon Martin in a highly charged case that inflamed impassioned debate over race relations.
A Florida jury voted Saturday to acquit Zimmerman, a decision that has enraged protesters who believe the killing -- and the verdict -- reflect a double standard in American society and justice that puts an extra burden on African Americans.
It has also put renewed focus on self-defense laws like Florida's "stand your ground" statute, which says people do not have to retreat when faced with the fear of death or serious bodily harm. Critics say Florida law made it too easy for Zimmerman to kill, and fear more such incidents now that he has been acquitted.
"Anyone walking or committing no crime can be followed or approached by another civilian and they can use deadly force and say it was self-defense," said the Rev. Al Sharpton, who announced Tuesday that rallies would be held in 100 cities on Saturday in support of federal civil rights charges against Zimmerman. "That is something that is frightening and cannot be allowed to sustain itself in our society."
Civil rights leaders and Martin's family have all called for peaceful protests. Police in Los Angeles praised one such rally Monday night in a city park.
But not all protesters have heeded the call.
On Monday, Los Angeles police arrested 14 people after protesters jumped on cars, kicked in windows, set off fireworks and possibly attacked someone, CNN affiliate KCAL reported.
The station said two members of its news staff were attacked while covering the demonstrations.
Protesters also pushed their way into a Walmart store in Los Angeles' Crenshaw district, throwing merchandise to the ground and causing other damage, the Los Angeles Times reported.
The scene Monday followed weekend protests in Los Angeles where demonstrators hurled rocks, batteries and chunks of concrete toward police. Officers responded by shooting bean bags. Police arrested seven people Sunday.
Amid the chaos Monday night, Beck took to Twitter to plead that "violence is never the answer."
He later warned that protesters who illegally block city streets will go to jail.
More than 550 miles to the northwest, in Oakland, California, scattered groups of protesters clashed Monday night with police.
Demonstrators threw rocks, bottles and firecrackers at police, Officer Johnna Watson said early Tuesday. Authorities arrested nine people, she said.
While some vandalism was also reported, it was mild in comparison to the damage from protests Saturday night, when demonstrators smashed windows and spray-painted several downtown businesses, CNN affiliate KPIX reported.
Civil rights leader John Mack said those behind the violence "have their own agendas that have nothing to do with justice, and very little to do with Trayvon Martin."
Memories of 1992
The Los Angeles area is particularly sensitive to violence in the wake of high-profile court decisions.
In 1992, widespread riots after the acquittal of Los Angeles police officers in the videotaped beating of Rodney King left more than 50 people dead.
Among the hardest hit areas was the Crenshaw district -- a predominantly African-American community that was the focus of Monday's unrest.
Los Angeles County Supervisor Mark Ridley-Thomas cautioned against demonstrations spiraling into deeper violence.
"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."
Los Angeles Mayor Eric Garcetti agreed.
"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."
Protesters marched peacefully Monday night in downtown Atlanta, chanting, "No justice, no peace," CNN affiliate WSB reported.
"I was devastated, a little bit heartbroken. But this is as much as we can do," protester Kennan Blair told the station.
In Cleveland, protesters gathered on the steps of the Cuyahoga County Justice Center carrying bags of Skittles -- the candy Martin had just bought before he was killed, CNN affiliate WEWS reported.
"I could have been Trayvon Martin," one African-American teen wearing a hoodie -- the same garment Martin was wearing -- told the station. "But this case isn't about racial issues. This case is about violence. This case is about the judicial system."
With anger and frustration over the verdict showing no signs of weakening, more protests are certain. On Tuesday, Sharpton said his National Action Network would organize rallies outside courthouses in 100 U.S. cities to protest the Zimmerman verdict and pressure federal authorities to act.
"We are going to fight," he said. "On Saturday night we lost the battle but the war is not over. And we intend to fight."
Many critics of Zimmerman''s acquittal are protesting not on the streets, but online.
As of Tuesday morning, more than 455,000 people had 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 27,000 signatures between them Tuesday morning. Petitions in support of Zimmerman had a few thousand signatures.
And someone created the "We Are Not Trayvon Martin" site on the popular blogging service Tumblr, drawing hundreds of essays from people angry or upset over the verdict.
"I think if I looked like Trayvon I could've been shot or arrested or antagonized and hated. I could've been dead at 17," wrote one poster who identified himself as a 31-year-old white man. "I think if Trayvon looked like me he could've grown up to be someone that did something wonderful for the world."
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."
CNN's Tina Burnside, Dottie Evans, Dave Alsup and Michael Pearson contributed to this report.
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