ST. LOUIS (AP) — Ferguson business owners and residents boarded up windows and cleared debris Wednesday after two nights of unrest — the second far less violent than the first — over a grand jury's decision not to indict a white police officer in the death of a black 18-year-old. Protesters continued to hold scattered demonstrations in the area.

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THE LATEST: Police in St. Louis locked down City Hall and called in more than 100 extra officers after several protesters rushed into the building yelling "Shame! Shame!" Three people were arrested, including one on an assault charge.

The demonstrators were among some 200 people who marched through downtown St. Louis and held a mock trial of Darren Wilson, the Ferguson police officer who shot and killed the unarmed Michael Brown during an Aug. 9 struggle in that St. Louis suburb.

In Ferguson, about a dozen people painted over downtown businesses' boarded-up windows while National Guardsmen looked on from posts along the street and on rooftops.

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THE OFFICER SPEAKS: In an interview with ABC News' George Stephanopoulos, Wilson said he feared for his own life when he shot Brown. He said there was nothing he could have done differently in the confrontation and disputed witness accounts that Brown at one point put his hands up in the air.

Wilson has been on paid administrative leave since the Aug. 9 shooting. He will remain on leave pending the results of an internal investigation pertaining to compliance with city and department policies and regulations, said Stephanie Karr, city attorney for Ferguson.

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THE BEGINNING: Wilson shot and killed Brown, who was unarmed, shortly after noon in the middle of the street after a scuffle. Brown's body lay there for hours as police investigated and a crowd of angry onlookers gathered. Several days of tense protests in the predominantly black community followed, prompting Missouri Gov. Jay Nixon to call in the National Guard. McCulloch decided to present the case to a grand jury.

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THE ANNOUNCEMENT: Made up of nine white people and three black people, the grand jury met 25 days over three months, and heard more than 70 hours of testimony from 60 witnesses. McCulloch held a prime-time news conference Monday to reveal the decision.

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THE DOCUMENTS: More than 1,000 pages of grand jury documents were released Monday, including Wilson's full testimony in which he described the scuffle in his patrol car and recognizing the cigars in Brown's hand as possibly being connected to a report of a convenience store robbery. Wilson also said that Brown approached him.

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THE FINAL SAY? The U.S. Justice Department has its own investigation into possible civil rights violations that could result in federal charges for Wilson, but investigators would need to satisfy a rigorous standard of proof. The department also has launched a broad probe into the Ferguson Police Department.