Some screamed. Some poured milk on their face.

Skin, slicked in sweat, burned from the chemicals in the pepper balls and pepper spray.

Chaos.

The final minutes of Tuesday's protests in Phoenix were a stark contrast to what had played out all day, a peaceful gathering of protesters from across a broad spectrum of social movements, just one block away from President Donald Trump’s first event since the deadly clashes in Charlottesville, Virginia.

A day later, videos and allegations continued to swirl on social media.

The question remains: What happened between riot police and demonstrators, in mere minutes, to cause the night to unravel?

Fingers are wagging both ways.

Police point to the protesters, claiming they were the first to launch tear gas, and that, in response, officers deployed their own.

Protesters point back, saying police attacks came unprovoked and without warning, not giving peaceful protesters — including children, the elderly and those in wheelchairs — time to leave the scene.

Five arrests were made, and no serious injuries were reported.

City officials say the events are under review by police. The Arizona chapter of the American Civil Liberties Union has called for an independent investigation into police conduct.

Protesters: 'It was unacceptable'

As the president's speech wrapped up inside, the chants started back up as the crowd anticipated rally-goers to exit behind the police line.

“No Trump! No KKK! No Fascists USA!” were among the chants, along with crowd favorite “Shame. Shame. Shame.“

Suddenly, with a loud bang, officers in riot gear swiftly began using aggressive crowd-control tactics.

Many in the crowd were stunned, with several people telling The Arizona Republic that they had no idea the show of non-lethal force was coming or why.

Several Republic reporters and photographers were at the scene where police deployed a series of what are called crowd-dispersal tools.

No reporters heard any clear warnings, and each described the situation devolving in a span of seconds — especially once a lit projectile thrown by someone in the crowd clearly struck a Phoenix police officer.

A group of churchgoers who earlier had led the crowd in gospel songs sprinted away from a clash between riot police and demonstrators.

Reyna Montoya, founder of non-profit organization Aliento, said police should have given more warning.

"I saw people who were in wheelchairs, people with babies, elderly people (hit)," she said. "It was unacceptable.”

Some protesters could be heard saying, “Time to leave.” Others dug in their heels, confused and frustrated about the display of force.

Kate Saunders described to The Republic how she carried a man for two blocks after he had fallen to the ground from the gas. “He started having an asthma attack, and his eyes were all bloodshot and he couldn’t see and he couldn’t breathe,” she said.

With a help of others they carried him to safety. But every time they stopped, the wave of smoke caught up, billowing over them.

“He kept reacting and reacting until he passed out,” she said.

Antonio Bustamante, a legal observer at the protest with the ACLU, said he did not see any demonstrators fire tear gas at police, although videos have surfaced on social media showing protesters trying to return gas canisters to officers.

"Well, I was there in the front, and nobody threw tear gas at the police," Bustamante said. "If the police were to hang their hat on that, then produce the canister, and we would all see that it would not be a canister from anyone other than the Phoenix Police Department.”

"It is hypocritical for the mayor of this city, Mayor Greg Stanton ... talking about how it was not OK for Donald Trump to visit this city and fanning the flames of Charlottesville and allow his Phoenix Police Department to abuse all the people who were here yesterday," Puente Arizona organizer Francisca Porchas said.

Porchas said Phoenix police officers were behaving an army, as they were "shooting (non-lethal ammunition) at people, macing people."

Police: 'We did warn people'

Authorities said the fragile peace came apart when protesters started throwing rocks, bottles and other projectiles at officers after the rally. Fights broke out, police said, within the crowd and people toppled pedestrian fencing that lined roadways and safety zones.

Phoenix police said that the first gas that was dispersed came from the crowd, not police. Sgt. Jonathan Howard said warnings were issued to break up the gathering.

The gasses and sprays first were used at Second and Monroe streets. Police then tried to disperse the crowd by forming a barricade and moving forward with riot gear.

Officers used smoke, pepper balls, pepper spray, tear gas and flash bangs. A casing for a blunt-force projectile called a foam baton was found on the ground, but Howard could not confirm the use of such projectiles. No rubber bullets were fired, according to Howard.

Before police made use of the smoke, Howard said, a field commander had warned officers that someone in the crowd had sprayed regular gas and instructed them to put on their gas masks.

Phoenix Police Chief Jeri Williams said she’s viewed several feeds of video of the confrontation and pushed back on allegations that police gave no notice before deploying their weapons.

“We did warn people,” Williams said in a Wednesday interview with The Republic. “Maybe you weren’t there to hear that or listen for that, (but) the air unit was overhead making announcements and warnings.”

Williams said some sort of “lighted device” was hurled at officers while they formed a line, and police were aware of a fight going on in the middle of the crowd. She also reinforced police officials’ statements Tuesday that gas was thrown on police by someone in the crowd.

Williams rejected the notion that the officers’ use of force was excessive.

“As a matter of fact, we restrained from using more force,” she said. “We didn’t rush the line, we gave people the opportunity to make the decision to (depart) and go home and create a peaceful scenario and situation.”

Williams stressed that of the “tens of thousands” of people who were downtown Tuesday night, only a small group created the dynamic that forced her officers to act.

“I know people are angry. There are some groups out there that are very angry with law enforcement,” she said. “I would challenge them to be angry with the people that created the dynamic that forced my officers to have to go in and create a situation where our city is safe, there’s no property damage and there were no major injuries to anyone.”

Model police policy: Warn in advance

The International Association of Chiefs of Police is widely viewed as the leading professional group for law enforcement agencies across the country. The group establishes “model” police policies adopted by agencies on topics that run the gamut, including crowd management and control protocol.

When it comes to crowds, pepper-derived devices “may be used against specific individuals engaged in unlawful conduct or actively resisting arrest, or as necessary in a defensive capacity when appropriate,” the policy reads.

“OC (pepper) spray shall not be used indiscriminately against groups of people where bystanders would be unreasonably affected, or against passively resistant individuals.”

Howard, the Phoenix police spokesman, said officers used progressively aggressive weapons for crowd control.

Police began with smoke, then balls of pepper spray, then escalated to stun grenades or "flash bangs," then pepper spray, then stronger gas, he said.

In such situations, the police chiefs' association policies state that an incident commander can authorize increasing uses of force, including higher-volume pepper spray. That spray is designed to be used in “civil disturbances against groups of people engaged in unlawful acts or endangering public safety and security,” according to the model policy.

A warning should be issued before deployment “whenever reasonably possible,” the policy said.

It should include “an announcement citing the offenses or violations being committed, an order to disperse, and designated dispersal routes,” and additional orders should be made before any action is taken, the policy said.

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