Nixon, for his part, said he would be making changes to help change the tone in the community, but he did not say what they would be. But he said it was crucial to allow protesters to express their anger so long as they respect the rights of others.
"We will not get the healing that we all need if the only response from the public is, 'Y'all just be quiet,' " he said.
Nixon traveled to Ferguson to appeal for calm after a night in which heavily armed police and protesters clashed. Wednesday's violence was the fourth straight night of unrest after Brown's shooting Saturday.
Nixon said he would visit the St. Louis suburb amid calls for continued protests and rising anger among residents about a lack of progress in the case and the treatment of protesters.
Police have also received harsh words from national media organizations after the brief arrest Wednesday of two reporters and the tear-gassing of an Al Jazeera America camera crew.
"The worsening situation in Ferguson is deeply troubling, and does not represent who we are as Missourians or as Americans," Nixon said in a statement Thursday. "While we all respect the solemn responsibility of our law enforcement officers to protect the public, we must also safeguard the rights of Missourians to peaceably assemble and the rights of the press to report on matters of public concern."
Nixon's statement comes after a fourth night of violent clashes between police and protesters that began Sunday with unrest and looting in the city on St. Louis' northern border.
After ordering protesters and reporters to turn off their cameras, police fired smoke bombs, tear gas and rubber bullets at protesters after some threw objects at them Wednesday, according to media accounts. CNN crews have not been ordered to turn off their cameras during the protests.
Twelve people were arrested, Ferguson police Chief Thomas Jackson said. Two officers were injured.
History of trouble
While locals say race relations have long been troubled between the city's mostly African-American population and the mostly white police force, anger spilled out after Brown's shooting death.
Police have released few details of what happened but have said the officer -- whose identity has not yet been made public by officials -- was defending himself against an effort by Brown to grab his weapon.
Jackson said the officer was sent to a hospital for treatment of facial swelling after the incident, but he did not say how he received the wounds.
Witnesses dispute police account
Witnesses paint a different portrait than that offered by police, saying Brown was running away when the officer first shot at him.
A town in turmoil -- 5 things about Ferguson, Missouri
Two witnesses told CNN on Wednesday that while Brown did appear to tussle with an officer before he was shot, he didn't enter the police cruiser as authorities say he did.
The women's accounts corroborate that of a previous witness, all three of whom said the officer fatally shot the unarmed teen.
Tiffany Mitchell told CNN she drove to Ferguson on Saturday to pick up an employee for work just in time to see Brown tussling at the window of a police vehicle.
She and the employee, Piaget Crenshaw, told CNN's Don Lemon on Wednesday about Brown's last moments.
"It looked as if Michael was pushing off and the cop was trying to pull him in," Mitchell said.
Crenshaw, still in her building, watched the same events from her window. She later shot cell phone video of the aftermath, which CNN obtained from affiliate KMOV.
It looked like the two of them were arm wrestling, she said.
Neither woman, who gave their statements to St. Louis County police, say they saw Brown enter the vehicle.
Instead, a shot went off, then the teen broke free, and the officer got out of the vehicle in pursuit, the women said.
"I saw the police chase him ... down the street and shoot him down," Crenshaw said. Brown ran about 20 feet.
"Michael jerks his body, as if he's been hit," Mitchell said.
Then he faced the officer and put his hands in the air, but the officer kept firing, both women said. He sank to the pavement.
After that, Crenshaw hit record on her cell phone. News of the killing spread fast through the neighborhood, and Brown's uncle walked up to the body to see if it was really his nephew, Crenshaw said.
The video shows police directing him back behind police tape.
(more on page 2)
While demonstrations over Brown's death were peaceful Saturday, they descended into violence, looting and dozens of arrests Sunday and Monday.
On Wednesday, police issued a statement saying they, too, mourned Brown's death, but warning protesters to clear the streets by dusk. They said provocateurs were taking advantage of the turmoil to seed the protests with violence.
While Wednesday's protest began calmly, it quickly grew tense as dusk approached.
Police assembled in tactical gear near the protesters, ordering them to disperse.
The St. Louis Post-Dispatch described police placing what it described as "high-caliber automatic weapons" on tripods atop armored vehicles and pointing them at protesters.
News photographers took snaps of young men lighting Molotov cocktails. And a CNN crew found spent crowd-control stun grenades lying in the street.
Police fired tear gas canisters at a crowd near a gas station that has turned into a gathering point for rowdy protests after dark.
Officers raised their guns at people heading for the protest, yelling for them to turn back.
As protesters scattered from the thick clouds of tear gas, officers in riot gear marched slowly in their direction to clear the area, ordering protesters and reporters filming to shut off their cameras, according to media reports.
A tear gas canister landed directly in front of the live television reporting position of Al Jazeera America; the crew ran, leaving its equipment behind. Then an officer later approached the camera and pointed it at the ground, CNN affiliate KSDK reported.
Al Jazeera America issued a statement calling the incident an "egregious assault on the freedom of the press that was clearly intended to have a chilling effect on our ability to cover this important story."
Earlier in the day, police detained and released two journalists -- Wesley Lowery of The Washington Post and Ryan Reilly of The Huffington Post -- who had been covering the shooting and the unrest. Neither was charged.
They said they were taken into custody at a McDonald's restaurant, where they were working, for failing to meet a police officer's deadline to pack up their gear and move.
"All of this went down, as you can see in the video, in less than two minutes," Lowery told CNN's "New Day."
"The idea that we posed any sort of threat because we weren't quickly enough packing up our bags is just ludicrous," Reilly told "New Day."
The Ferguson police chief said he did not know the detaining officers, adding: "We had a lot of different agencies out there."
The Huffington Post accused police of "false arrest" and "militant aggression" against the reporters. Washington Post Executive Editor Martin Baron said "there was absolutely no justification" for the arrest of his newspaper's reporter.
Police also detained St. Louis Alderman Antonio French, who has posted a continuous stream of protest video to social media. He was released Thursday morning, he said.
In all, police arrested 12 people -- including the two reporters -- Wednesday night, Jackson said, bringing the total since the weekend to 65. He had previously said 18 people had been arrested. Two police officers were injured Wednesday night, Jackson said.
'Just in shock'
Much of the anger among protesters has been directed at officials who have refused to release the name of the police officer who shot Brown. Officials say police officers, and others in the administration and police force, have been subjected to death threats.
On Wednesday, the American Civil Liberties Union of Missouri filed a lawsuit seeking the release of the officer's name under the state's open records law.
It's unclear whether the suit will succeed. Missouri law provides a specific exemption barring the release of records that authorities conclude are "likely to pose a clear and present danger" to victims, witnesses or others.
On Thursday, the shadowy activist group Anonymous published the name of the officer it believes responsible for the shooting. Earlier, the group claimed to have hacked the city servers and obtained dispatch recordings and other information.
Jackson later said the group had the wrong officer. CNN is not reporting the name.
In addition to an investigation into Brown's shooting being led by St. Louis County police, federal civil rights investigators and the FBI are carrying out their own inquiries.
President Barack Obama, who earlier this week appealed for calm, has also been briefed on the situation, according to the White House.
Jackson said that he will meet with Brown's mother, the NAACP and a Department of Justice representative Thursday.
Brown's family is frustrated with the lack of information from police, said their attorney, Benjamin Crump.
"Like all the people in that community and many people around the country, they're just in shock that this could happen to an unarmed teenager in broad daylight," he told CNN. "It makes no sense, and they feel there's no way it could be justified."
Copyright 2015 Nexstar Broadcasting, Inc. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed.