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Authorities in Missouri pleaded for calm Monday night as the anxious city of Ferguson waited for a grand jury’s decision on whether to indict the white police officer who shot and killed Michael Brown, an unarmed black teenager, three months ago.

Businesses boarded their windows, the National Guard was at the ready, and schools closed for the following day. Several hundred people gathered at Ferguson police headquarters, chanting. Gov. Jay Nixon pledged that law enforcement would focus on protecting lives, property and free speech.

“Our shared hope and expectation is that, regardless of the decision, people on all sides show tolerance, mutual respect and restraint,” he said.

Charlie Dooley, the St. Louis County executive, was more blunt: “I do not want people in this community to think they have to barricade doors and take up arms,” he said. “This is not a time to turn on each other. This is a time to turn to each other.”

The county prosecutor, Bob McCulloch, scheduled a 9 p.m. ET press conference to announce whether the grand jury would indict Officer Darren Wilson, who gunned down the teenager on a Ferguson street.

There was no indication what the decision might be — the grand jury had options from first-degree murder to no charge at all — and even the governor said he did not know.

Benjamin Crump, a lawyer for the Brown family, told MSNBC that the relatives were “praying for an indictment, and they’re trying to put their faith in the justice system.”

Don't let fear or violence further divide our city. Reject both. Pray for peace. Work for justice. Push for change. — Antonio French (@AntonioFrench) November 24, 2014

Wilson, 28, shot Brown, 18, during a confrontation on the afternoon of Aug. 9. In the days that followed, Ferguson, a once-obscure St. Louis suburb, was rocked by clashes between demonstrators and police with military-style equipment. The grand jury has been weighing evidence for three months.

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Ahead of the grand jury decision, the governor declared a state of emergency and activated the Missouri National Guard. Authorities and lawyers for the Brown family encouraged both police and protesters to maintain calm.

“The world will be watching us,” said St. Louis Mayor Francis Slay. “St. Louis finds itself with an opportunity to show a nation the ways in which a community can be more fair and more just for everyone. We must seize this opportunity for everyone.”

St. Louis County police put out a call for donations, including water, cough drops and gift cards to pay for meals, for police working around the clock.

QuikTrip closed four locations in and around Ferguson before the grand jury announcement, a spokesman said. A QuikTrip in Ferguson was burned during the demonstrations in August.

“We don’t understand why it took so long,” Rick Canamore, 50, a pharmaceutical worker from Normandy, Missouri, who is black, said at Ferguson police headquarters. “If Mike Brown shot Darren Wilson, he’d be in jail by now.”

Sasha Winslow, 48, a flight attendant from Ferguson, who is also black, said she would be unhappy if there was no indictment.

“My stomach is tight,” she said. “I’m anxious, yet fearful, yet hopeful.”

The grand jury is composed of six white men, three white women, two black women and one black man, selected at random from St. Louis County, which is about 70 percent white. Ferguson, a city of 21,000 people, is about two-thirds black. It takes nine of 12 votes to indict.

Accounts of the shooting they investigated have varied. Wilson told investigators that there was a struggle for his gun inside his SUV, and that Brown pressed the barrel against the officer’s hip, according to an account in the St. Louis Post-Dispatch attributed to a knowledgeable source.

Brown ran away. The officer claimed that he fired again outside the police SUV after Brown turned back and charged at him, according to the account provided to the Post-Dispatch.

Witness accounts differ. Dorian Johnson, a friend of Brown’s who was there, told MSNBC that Wilson grabbed Brown by the neck in the SUV. Later, when Wilson fired the fatal shot, Brown was facing Wilson and had his hands up, Johnson said.

Another witness, Tiffany Mitchell, told MSNBC that Brown was shot with his hands up. The Washington Post reported that more than six black witnesses gave testimony to the grand jury that mostly supports the officer’s account.

Ferguson police said after the shooting that Brown was suspected of stealing a box of cigars from a convenience store minutes earlier, and police dispatch audio obtained by the Post-Dispatch showed that Wilson had offered to help look for the suspect.

The Justice Department is conducting a separate civil rights investigation, including a review of the overall practices of the Ferguson police.

Wilson has not appeared in public since the shooting.

Rick Brown and Tracy Jarrett contributed to this report.