Six people who spent the night in the King County Jail face misdemeanor charges that include obstructing officers, resisting arrest, property damage and failure to disperse, the City Attorney's Office said.
Three who bailed out of the jail could be charged later, and five others were expected to make their initial appearances in King County Superior Court to face more serious charges later Thursday.
In all, 17 people were arrested after the "anti-capitalism" demonstration turned violent, with protesters pelting police with rocks and bottles and police firing flash-bang grenades and pepper spray.
Resisting arrest is punishable by up to 90 days in jail and a $1,000 fine. Obstruction of an officer, property damage and failure to disperse are gross misdemeanors, punishable by up to a year in jail and a $5,000 fine.
Eight officers suffered minor injuries, police said.
The "anti-capitalism" protest followed a peaceful immigration reform march and rally that drew a much larger crowd of thousands earlier in the day.
It was the second year in a row for May Day violence in the Emerald City; last year, vandals smashed the windows at several downtown banks and stores, prompting criticism that the Seattle Police Department was unprepared.
On Wednesday evening, officers used "flash bangs" and pepper spray against dozens of protesters who threw construction street barriers, trash cans and newspaper bins on the streets in an attempt to block advancing police officers. A few protesters smashed windows of local businesses.
"We're a bigger and better city than this. I look at this and I am disappointed that this is the picture the world sees of us," Seattle Mayor Mike McGinn said late Wednesday.
Police used their bikes to shield businesses and eventually began to use "flash bang" grenades — releasing a flash of light, smoke and a loud noise — to disperse the crowd. But that pushed the group to the Capitol Hill neighborhood, and they left a wake of overturned trash cans and debris on the street.
There were no immediate cost estimates from damage.
The injured officers suffered mostly scrapes and bruises, said Police Capt. Chris Fowler. One officer was hit by a rock on her knee.
Initially, the protesters concentrated on a business sector of downtown Seattle. Despite lacking a permit to march, Seattle police escorted them.
"That first march came downtown. It was absolutely peaceful. ... It was almost a festive affair and they had some serious messages, too, that they wanted to express. No incidents whatsoever," McGinn said. "The second march was very different, and it wasn't just merely because it was unpermitted. I think it also had to do with the nature of the individuals in it and what they wanted to do."
During last year's May Day demonstrations, anarchists broke windows of vehicles and store fronts, including Niketown, and used smoke bombs. Protesters also targeted a federal court building, breaking windows and doors.
Olivia One Feather, of Covington, joined the crowd Wednesday night because she wanted to see how police handled the protest. She said she wasn't impressed, adding that she was pepper sprayed in the face while trying to video record officers.
Of the protesters, she said, "They're doing what we need to do to stand up to ourselves. These are our streets and we have the right to take them."
Many of the protesters were self-described anarchists. A local anarchist website said protesters would attempt to disrupt May Day.
After the clashes died down, local residents were seen cleaning up trash left by protesters.
The violence marred a May Day that immigrant-rights activists hoped would put a focus back on immigration reform. Thousands of people marched about 2 1/2 miles from the Central District toward Seattle's downtown Jackson Federal Building after a May Day rally supporting immigrant rights and labor.
Many carried signs, with messages such as "We are America," and "There are no illegal humans." One sign suggested forgetting about marijuana and instead asking the United States to "Legalize my mom," a reference to Washington's recent legalization of marijuana.
Other demonstrations and rallies in Olympia, Mount Vernon, Spokane, Vancouver, Walla Walla, Wenatchee and Yakima went peacefully.
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