FERGUSON, Missouri – A peaceful demonstration over the killing of an unarmed black teenager turned violent Wednesday as police in paramilitary fatigues and riot gear tear-gassed dozens of protesters, fired stun grenades into a crowd and arrested reporters in a third night of chaos in the aftermath of the police shooting of Michael Brown.

Close video Riot police using tear gas in Ferguson Msnbc.com reporter Trymaine Lee, who was tear gassed by police officers, describes the breaking news scene. Msnbc.com reporter Trymaine Lee, who was tear gassed by police officers, describes the breaking news scene. share tweet email Embed

Young black men and women protesters, with their hands held high in the air, had refused to heed police orders to disperse as the sun set on this St. Louis suburb of 20,000. While there had been some taunts from the crowd, no one appeared armed and there was no evident threat to police. But as darkness descended, forces moved in, announcing on a bullhorn that the gathering was no longer peaceful and began firing tear gas and stun grenades, choking protesters lined along a main thoroughfare in Ferguson.

Many protesters raced away, gasping for air, screaming, tearing up or vomiting as the gas produced a burning sensation in their eyes and on their skin. Heavy smoke filled the air for hours, illuminated in the darkness by flashes of light produced each time that a stun gun or noise grenade was fired.

The protests in the West Florissant section of the city, by most accounts, appear to have been nonviolent. Some church groups, a gospel choir and residents of all ages had gathered at the area around 7 p.m. local time near to where Brown was killed Sunday night. But within an hour a massive police force, on foot and in armored vehicles descended on the area demanding the crowd’s dispersal.

Police scoured the area for reporters, ordered some to cease filming or reporting. Ryan Reilly of The Huffington Post and Wesley Lowery of The Washington Post were arrested for reasons that remain unclear. Both reporters have since been released without any charges.

Reilly, according to a statement from The Huffington Post, was “working on his laptop in a McDonald’s near the protests in Ferguson when police barged in, armed with high-power weapons and began clearing the restaurant.”

Reilly photographed the intrusion and police demanded his identification in response, the statement said. Reilly began packing up his belonging and “was subsequently arrested for not packing up fast enough.” The statement said both Reilly and Lowery were assaulted. Msnbc reached out to the Ferguson Police Department for comment but has not heard back at this time.

Protests have engulfed Ferguson since Brown was shot and killed by an as-yet unidentified white officer on the Ferguson police force. Many questions about the killing remain unknown. In an interview earlier Wednesday, Ferguson Police Chief Thomas Jackson told msnbc he wanted to find out the truth about the killing. But police have yet to interview the main eyewitness and will not release details such as how many times Brown was shot or details from his initial autopsy report.

The U.S. Attorney’s office announced earlier Wednesday that it had launched a civil rights investigation into the circumstances surrounding Brown’s death and urged witnesses to contact the FBI with any information.

The Ferguson-Florissant School District postponed its first day back to school from August 14 until August 18 “in response to concerns expressed by many about continuing unrest in our community.”

Jackson held a press conference on Wednesday, curiously at the same time as a peace march nearby. He said the Justice Department and local NAACP were coordinating a meeting between Ferguson police authorities and the Brown family.

“Race relations is a top priority right now,” Jackson said earlier in the day. He later said he was open to guidance on how to improve tensions within the Ferguson community: “Tell me what to do and I’ll do it.” Ferguson, a leafy bedroom community outside St. Louis, was not in the national spotlight before Brown’s killing. But the teenager’s death has revealed a town riven by racial strife and dominated by a predominately white and heavily militarized police force with a record of focusing its attention almost exclusively on the town’s African-American community.

Black residents say officers routinely harass them and that an old-boys network has kept the department from hiring more officers of color.

The scene late Wednesday resembled more of an urban war zone however with residents fleeing in freight, heavy smoke plumes hanging low to the ground and reporters forced to shut off their cameras.

Lowery, who says his Post credentials were around his neck, believes his decision to use his phone to videotape the officers angered them, and when he inquired about which way to exit the premises – in what Lowery says was an attempt to follow the officers’ instructions – his bag slipped off his shoulder. As Reilly reached to collect his bag, one officer said “Let’s take him,” according to Lowery. “They slammed me into a soda machine,” he said, adding “By my standards, I call it assault.” Close video Reporter describes arrest in Ferguson police crackdown Wesley Lowery, Washington Post reporter, describes the circumstances of his arrest in Ferguson, Missouri, where peaceful protests over the police killing of Michael Brown were met with a militarized police show of force. Wesley Lowery, Washington Post reporter, describes the circumstances of his arrest in Ferguson, Missouri, where peaceful protests over the police killing of Michael Brown were met with a militarized police show of force. share tweet email Embed

The Post released a statement following Lowery’s arrest. The paper says Lowery “was illegally instructed to stop taking video of officers. Then he followed officers’ instructions to leave a McDonald’s - and after contradictory instructions on how to exit, he was slammed against a soda machine and then handcuffed. That behavior was wholly unwarranted and an assault on the freedom of the press to cover the news. The physical risk to Wesley himself is obvious and outrageous”

“The chief thought he was doing you a favor” - police officer tells me about release. With no charges, no police report — Wesley Lowery (@WesleyLowery) August 14, 2014

According to the Post, “after being placed in a holding cell, he was released with no charges and no explanation. He was denied information about the names and badge numbers of those who arrested him.”

Shortly after the arrest, Reilly told msnbc’s Chris Hayes that the arresting officer slammed his head against glass deliberately before apologizing sarcastically in what Reilly called “a terrible experience.”