Yamiche Alcindor

USA TODAY

FERGUSON, Mo. — Missouri Gov. Jay Nixon activated the state's National Guard and declared a state of emergency Monday, his first move to prepare for possible backlash to a grand jury decision in the case of a white police officer who shot and killed a black teenager.

The emergency order, in effect for 30 days, instructs St. Louis County Police Department, Missouri State Highway Patrol and St. Louis Metro Police to work together in a unified command to keep the peace should public reaction to the decision turn violent. It puts the county police, rather than Ferguson police, in charge of security in Ferguson if unrest develops in the St. Louis suburb.

The governor directed police "to protect civil rights and ensure public safety in the city of Ferguson and the St. Louis region."

"This is America. People have the right to express views and grievances, but they do not have the right to put fellow citizens and property at risk," Nixon said last week. "Violence will not be tolerated."

The National Guard will provide security at command posts, fire stations and other government buildings to leave police officers free to attend to regular service calls, St. Louis Police Chief Sam Dotson said.

The order comes as the area waits to learn whether a St. Louis grand jury will indict officer Darren Wilson, 28, in the shooting death of Michael Brown, 18, an African American. Police, city officials, schools, businesses and protesters have been meeting daily in an effort to avert repetition of the chaos that immediately followed the Aug. 9 shooting, when protesters clashed, sometimes violently, with police.

The grand jury convened Aug. 20 to hear evidence in the case. At issue is how Brown died. Police say Brown struggled with Wilson inside his police car, then reached for Wilson's weapon. Brown's family and some witnesses say Wilson killed Brown as he raised his hands in surrender.

"Regardless of the outcomes of the federal and state criminal investigations, there is the possibility of expanded unrest," the order said. "Our citizens and businesses must be protected from violence and damage."

Randy Reep, a criminal defense attorney and former prosecutor in Florida, said the governor's actions signal he may know what the grand jury decided and that he expects no indictment. He said it would be judicious, and not a violation of state law, if prosecutors let the governor and other authorities know in advance so they can prepare.

"There is unlikely to be riots if they indict the officer. But there certainly is going to be unrest, like we saw in months previous, if the grand jury comes back and says we are not going to indict," Reep said.

DeRay Mckesson, one of the most visible supporters of Brown's family, thinks Nixon's move to activate the guard and declare an emergency is excessive in light of months of largely peaceful protests.

"Gov. Nixon has shown that the police prepare for the assembly of black bodies as if they are preparing for war," Mckesson, 29, of Minneapolis, Minn., said. "I think it's an incredible overreaction to unrest that hasn't occurred. There is no need for a state of emergency right now."

This is the second time Nixon ordered a state of emergency relating to Brown's shooting. This summer, Nixon declared the status, instituted a curfew and later called in the National Guard as demonstrators overran Ferguson.