By the time he picked up a plastic water bottle, wound his arm back and let it fly over the heads of protesters toward a row of federal police officers in riot gear, Daquan Jones had been pushed, pepper-sprayed and gassed with a chemical that made his eyes tear and his throat burn.

Jones, 23, a lifelong District resident, joined the third day of protests over police use of force and the killing of George Floyd around lunchtime Sunday. He came to march and chant, to pour his own rage and sorrow into a cause where, he hoped, it might be useful.

He didn’t bring goggles. He didn’t think he’d need a helmet.

But as darkness fell over hundreds gathered at Lafayette Square and police pelted the crowd with pepper pellets, Jones said he looked at the plastic water bottle in his hand and decided it was time to throw something back.

“At the end of the day, they got shields. What do they care?” he said. “They’re dodging water bottles while we’re out here dodging bullets.”

In trying to pin down the source of chaos, public officials blamed agitators who came from outside the city. Others, such as Mayor Muriel E. Bowser (D), said a small “organized group” had come into the District bent on destruction. But several demonstrators and experts who study protest movements said the truth is more complicated.

While a small group of people had come with baseball bats and fireworks, lighter fluid and hammers, dozens more who participated in the destruction that littered the city with broken glass and defaced storefronts joined in only after hours of confrontation, as their outrage and scorn rose from a simmer to a rolling boil.

Looking at demonstrators as one singular group with one unified mission oversimplifies protests and who tends to show up at them, said Dana R. Fisher, a University of Maryland sociology professor who studies protests and social movements.

“There are Black Lives Matter protesters who have been shoved one too many times by the police and are fed up. There are the anarchists who came there to smash capitalism and tear down Starbucks to make way for whatever comes next,” she said. “There are the folks who genuinely want a peaceful protest and all the young people who have over the last several years gotten really good at civil disobedience, which, by the way, does not include throwing rocks at police.”

After weeks of economic devastation wrought by shutdowns that have shuttered businesses and pushed the national unemployment rate to nearly 15 percent, Fisher said, those who might not have otherwise participated in looting may have joined in when the opportunity presented itself.

“Particularly now when the economy is in free fall, you may have people thinking, ‘Well, the window is already broken, people are already taking things, maybe I’ll grab something I need,’ ” Fisher said. “It’s taking advantage of an opportunity.”

While there is overlap among the groups, she added, and the categories are fluid, President Trump and others have flattened them into one, Fisher said, conflating groups that might not agree on tactics or why they are participating.

On Sunday afternoon, the Trump administration intensified its effort to pin blame on the far-left “antifa” movement for escalating demonstrations, property damage and violence. The president vowed on Twitter to designate antifa a terrorist organization, and Attorney General William P. Barr said it and other groups’ activities constituted “domestic terrorism” — neither of which is possible, for practical and legal reasons.

D.C. police said Monday that officers made 88 arrests related to the protests Sunday and overnight, and that two-thirds of those charged are facing felony counts for looting and destruction of property. Police Chief Peter Newsham said investigators are reviewing surveillance footage and that more arrests are possible.

He said seven police officers suffered minor injuries Sunday night. Damage was most extensive around Lafayette Square near the White House, but it extended to Northeast Washington, Georgetown and upper Northwest.

In an attempt to wrest control of the chaos that has gripped the District in recent nights, Bowser imposed a curfew beginning 7 p.m. Monday and Tuesday — four hours earlier than Sunday.

Though tense, the mood remained mostly calm Sunday night as demonstrators marched around the White House before reconvening at Lafayette Square. Three hours before the curfew, cellphones chimed with the Districtwide alert that warned people to go home.

“F--- your curfew,” the crowd chanted.

Near the back, someone lit an American flag on fire. Then the door of a park maintenance building was kicked in. Another fire, more pepper pellets, another wave of gas.

Thick smoke and fumes hung over Lafayette Square like a sheet as waves of demonstrators ran to get out of the tear gas and away from advancing police, pulling at masks meant to protect them from the still-raging coronavirus pandemic and coughing into the night air.

Jones, a college graduate with a marketing degree, said he decided to leave when police began to force people out of the park. He and his cousin walked around downtown, surveying the damage in a haze of disbelief.

“I felt like I was looking at pictures from a history textbook,” he said. “I don’t necessarily agree with lighting things on fire, but I get why people are doing it. They’re tired of being calm and just using their voices. When you don’t feel heard, you feel like you need to take an extreme step to get people’s attention, and that’s what people are doing now.”

Some demonstrators, tired of reaping the consequences of other people’s more destructive actions, eventually took to patrolling their own side.

About 1 a.m. Sunday, Arianna Evans, 23, of Bowie, Md., lifted the speaker of a megaphone to her lips — one she had been using to beg officers to take a knee, to acknowledge the humanity in the black faces that stood before them — and turned away from the line of police to admonish the demonstrators around her:

“Stop throwing [stuff],” she shouted. “Put the bottles down!”

Later that day, a group of black men marching blocks from the White House converged on a white man dressed in all black who had begun to chip away at the sidewalk with a hammer. They picked him up as he thrashed and writhed and hauled him over to the police line.

“He’s yours,” they shouted. “Take his a--.”

Evans said she worried the vandalism was hurting the message of the peaceful protesters who made up the majority of the crowd.

“Violence is not the answer, and the more that we are violent the worse this will get for every one of us who is out here,” she said. “It’s very disappointing to me that we have to deal with this agitation, which feels like it’s not even from people who genuinely care about our lives, about our livelihoods, about social and economic equality.”

As Sunday melted into Monday morning, Autymn Bradshaw, 20, a college student from Howard County, ran from officers in a crush of screaming protesters, who began to call for “white bodies to the front.” She put herself nearest to the police line, in front of black protesters like Evans, an Army veteran who is starting classes at Howard University in the fall.

Bradshaw cried as she stood with her hands raised. When police pressed forward, she ran, afraid they might start shooting plastic bullets or pepper balls. It was her first protest, she said, and she hadn’t expected to be so scared.

“I was thinking, ‘What are they going to do to us? What’s going to happen? Are they going to shoot us? Are they going to tear gas the crowd?’ ” she said, as she readied herself to head back to Monday’s protest.

This time, she said, she’s going to be ready. This time she’s bringing goggles.

Rebecca Tan, Peter Hermann, Antonio Olivo and Rachel Chason contributed to this report.