JEFFERSON CITY, Mo. >> As a grand jury weighs possible criminal charges against the police officer who fatally shot Michael Brown, Missouri’s governor has again activated the National Guard in an effort to avoid more unrest in the St. Louis suburb of Ferguson.

Unlike in August, when Gov. Jay Nixon asked the troops to help provide security after protests turned occasionally violent, his latest move is pre-emptive. It comes ahead of any decision on whether Ferguson Police Officer Darren Wilson, who is white, will be indicted for the Aug. 9 shooting death of the black 18-year-old.

There also are some operational differences this time. When Nixon last declared a state of emergency, he put the Missouri State Highway Patrol in charge of a unified local police command and later activated the National Guard to provide security around the command center.

This time, Nixon said the St. Louis County Police Department would be in charge of security in Ferguson and would work with the Highway Patrol and St. Louis city police as part of a unified command to "protect civil rights and ensure public safety" in other jurisdictions.

"My hope and expectation is that peace will prevail," Nixon said Monday. "But we have a responsibility — I have a responsibility — to plan for any contingencies that might arise."

There is no specific date for a grand jury decision to be revealed, and Nixon gave no indication that an announcement is imminent. But St. Louis County prosecutor Bob McCulloch has said that he expects the grand jury to reach a decision in mid-to-late November.

The U.S. Justice Department, which is conducting a separate investigation, has not said when its work will be completed. It’s looking into potential civil rights violations in Wilson’s actions and the police department’s overall practices, including whether officers used excessive force and engaged in discriminatory practices.

The governor did not indicate how many National Guard troops would be mobilized, instead leaving it to the state adjutant general to determine. Nixon said the National Guard would be available to carry out any requests made through the Highway Patrol to "protect life and property" and support local authorities. If the Guard is able to provide security at police and fire stations, then more police officers may be freed up to patrol the community, Nixon said.

St. Louis Mayor Francis Slay said Monday that he supports Nixon’s decision to activate the Guard. He said the Guard "will be used in a secondary role" and could potentially be stationed at places such as shopping centers and government buildings.

"The way we view this, the Guard is not going to be confronting the protesters and will not be on (the) front line interacting directly with demonstrators," Slay said.

On the day of the shooting, Wilson had spotted Brown and a friend walking in the middle of a street and told them to move to the side, but they did not. According to a St. Louis Post-Dispatch report based on sources the newspaper did not identify, Wilson has told authorities he then realized Brown matched the description of a suspect in a theft minutes earlier at a convenience store. Wilson backed up his police vehicle and some sort of confrontation occurred before Brown was fatally shot. He was unarmed and some witnesses have said he had his hands up when he was killed.

Brown’s shooting stirred long-simmering racial tensions in Ferguson, where two-thirds of the residents are black but the police force is almost entirely white. Rioting and looting a day after the shooting led police to respond to subsequent protests with a heavily armored presence that was widely criticized for continuing to escalate tensions. At times, protesters lobbed rocks and Molotov cocktails at police, who fired tear gas, smoke canisters and rubber bullets in an attempt to disperse crowds.

Associated Press writer Summer Ballentine contributed to this report.