Los Angeles on Saturday joined more than 100 other US cities in protesting against the acquittal of George Zimmerman, who shot dead unarmed black teenager Trayvon Martin.

Hundreds of demonstrators gathered in front of the downtown US Federal Court building for a nationwide vigil calling on the US Justice Department to bring a civil rights case against Zimmerman.

Although demonstrators chanted "No justice, no peace," the vigil and demonstration were generally peaceful, with heavy police presence and helicopters hovering over the sky.

The signs held by the demonstrators showed their demand and anger.

"Racism is alive and well in America, Zimmerman is a cold blooded murder. Thanks to a racist jury, he walked free," the sign echoed the voice of many demonstrators.

"One child or one teenager is hurt, the whole nation is hurt," said another sign.

"You don't have a 2nd Amendment right to commit 2nd degree murder," a mother held her sign.

Some demonstrators criticized the US Justice Department by holding signs such as "There will be no justice from the Department of Justice."

"I am here to support the black community and all workers in general for the treatment of Trayvon Martin who was murdered. But the issue is bigger than that. The system is set up so that happens," Michael Kakes told Xinhua.

"It was Martin today, but it could be anybody of colors. I am here to show solidarity to change the system because the system is killing people everyday," said Kakes, who was among hundreds of demonstrators.

Kakes is a white himself. He said the case is racially motivated, and the system is built on racism because without racism they can not divide the people, black and white, men and women."

"We want to show that together we can defeat that kind of staff. That's why I am here," said Kakes.

Shark Jacquescarr, an African American, said that he thought the prosecution made a mistake to have all six jurors white without any black person.

He said he was shocked when he learned that Zimmerman was not found guilty, but he though it was not the problem of racism but the problem of the justice system.

He said there is nepotism in the justice system because Zimmerman had relatives in the justice system and that should be stopped.

He suggested that the US justice system should be supervised and committees formed by people from different ranks should watch closely the police and judges to see whether they are doing justice.

Dorsey Brickwood, an 87-year-old African American woman on her wheelchair, said that she was there because she had seen injustice for so many years and she had enough.

Asked what kind of changes she was expecting, the woman said: "I don't know how we can change, but I do know that we must change, and we have to come together to make the change because all those minorities suffer in their own ways under the system."

Other cities in Southern California like Riverside and San Bernardino held similar protests on Saturday.

"This type of thing goes on every day in America, as far as black kids being killed at the hands of someone of another race or black kids being killed at the hands of someone of their own race, " Eddy Moss, who is organizing the San Bernardino protest, was quoted as saying.

Moss said the verdict in the trial would have been different if Zimmerman had been black and Trayvon had been white.

Carolyn Huyck, organizer of the Riverside protest and vigil, said she had never organized a protest or even attended one.

Huyck, 34, like many others, said she believes that Zimmerman saw a young black male and racially profiled him as someone who was doing something wrong.

Zimmerman, a neighborhood watch volunteer of 28 years old in Florida, was charged with a second degree murder for shooting 17-year-old African-American high school student Martin to death in February last year.

A jury in Florida acquitted Zimmerman last Saturday which triggered heated debates over whether there is injustice against minority in the case.

Demonstrations were held during the past week in several US cities, including Los Angeles, New York and Oakland.