Ferguson, Missouri (CNN) -- The morning after a peaceful candlelight vigil for a teenager fatally shot by police disintegrated into violence and looting, the mayor of Ferguson, Missouri, called for calm.

"Obviously, the events of last night are not indicative of who we are," James Knowles said on CNN on Monday morning, adding that the chaos that erupted Sunday night in the St. Louis suburb was "not constructive" and was only "bringing down the community."

A short time later, a crowd gathered in front of the Ferguson Police Department to protest the killing of 18-year-old Michael Brown by a city police officer Saturday.

Led by a man carrying a bullhorn, the crowd shouted, "No more, no more!" Dozens of people walked through the streets of Ferguson shouting, "No justice, no peace!"

Monday's gathering was peaceful, but Sunday evening in Ferguson was a far different scene. What began as a vigil for Brown ended with 32 people arrested and shots fired at police, a St. Louis County Police spokesman said Monday.

Witnesses to Brown's shooting said he had been unarmed and had his hands in the air.

Authorities told a different story. The police officer tried to get out of his vehicle just before the shooting, but Brown pushed him back into the car, said St. Louis County Police Chief Jon Belmar.

Brown "physically assaulted" the officer, Belmar said, and the teen tried to get the officer's weapon. Brown was shot about 35 feet from the vehicle, the chief said, declining to provide more details.

"The genesis of this was a physical confrontation," he said, adding that his department has been called in to conduct an independent investigation.

Ferguson Police said its cars are not equipped with dashboard cameras.

Shell casings collected at the scene were from the officer's weapon, Belmar said.

Anger over the shooting gripped many in Ferguson. Michael Brown's mother, Lesley McSpadden, was emotional as she shouted into a television reporter's microphone.

"You took my son away from me! You know how hard it was for me to get him to stay in school and graduate? You know how many black men graduate? Not many!" she said. "Because you bring them down to this type of level where they feel they don't got nothing to live for anyway! (They feel) they gonna try to take me out anyway!"

Social media were on fire Monday as people are posting strong opinions about the incident. #MichaelBrown and #Ferguson were trending topics.

Confrontation with police

During the vigil Sunday, some shouted at police.

Stoic officers in riot gear watched as young men knelt before them, hands up to symbolize surrender.

But one officer can be heard on video yelling back, calling protesters "animals."

"We will stay out here as long as you are!" protesters screamed at police.

Demonstrators held their hands in the air and chanted, "We are Michael Brown." Others held signs that said, "No justice, no peace." Another sign read, "Police stops should not = dead kids."

The gathering became more intense as some people broke windows at a store and began taking things from it. They threw rocks and bottles. Gunshots rang out.

Antonio French, an alderman in St. Louis, said a QuikTrip gas station was looted and an ATM dragged out.

"This QuikTrip is where things started (Saturday) with this case, based on various accounts," French said.

The slain teenager and a friend were "accused of stealing gum from the store or some sort of cigarettes," the alderman said.

Mayor wants independent investigation results

"Last night, everything lost control," Knowles said Monday on CNN's "New Day."

He was asked about the officer who called protesters "animals."

"The officers did their best. They're only human," Knowles responded, adding that not every police officer present was from the Ferguson department.

Knowles said he wants to let the independent investigation into Brown's death take its course. He plans to meet with Brown's parents soon and will meet this evening with clergy in Ferguson and African-American leadership in the town.

Whatever the investigation's findings, "we will deal with that," he said.

Multiple gunshots

A medical examiner will issue a ruling on how many times Brown was shot.

"It was more than just a couple," Belmar said.

Witnesses said Brown did nothing to instigate the shooting and appeared to be surrendering when he was killed. Brown was spending the summer in the neighborhood with his grandmother Desuirea Harris, she told KMOV.

"My son just turned 18 and graduated high school and he didn't bother nobody," his mother, Lesley McSpadden, told CNN affiliate KSDK.

Brown was supposed to start classes at Vatterott College on Monday, she said.

"People have a lot of anger and are frustrated," French said. "They don't have recourse in the system, and it happens often in this country, and it has boiled over. I think people are angry and looking for a reason to let it out tonight."

Family retains Trayvon Martin lawyer

"We don't know what happened, and there are lots of conflicting stories," Knowles said. "Unfortunately, there will have to be some time taken to understand what happened. Hopefully, we will get to an understanding, and justice will be served."

The officer who shot Brown is on paid administrative leave during the investigation and will be available to talk to county homicide detectives.

He has been with the force for six years and will be required to undergo two psychological evaluations before returning to duty, Belmar said.

U.S. Attorney General Eric Holder has instructed the Justice Department's civil rights division to monitor the developments in the case.

The FBI said it is assisting police in its investigation and will review the findings.

Benjamin Crump, the lawyer who handled Trayvon Martin's case, will represent the family. Martin, 17, was killed in 2012 by a Florida neighborhood watch organizer, who was acquitted of murder charges.

it's really sad, read it on LIB, the rate this Racist Cops be taking down black Kids though ...just pathetic. how will 18 and Unarmed kid disarm you for christ sake. wish y'all see the pic of the teen.