The FBI and other federal agencies have sent teams of agents and officers to Ferguson ahead of a grand jury decision on whether a white police officer will be charged in the death of Michael Brown, whose killing Aug. 9 ignited a firestorm of controversy and sparked protests and unrest.

The FBI did not say how many people it has sent to the St. Louis suburb, but federal officials said they would not be assisting with crowd control or making arrests for disturbing the peace, vandalism, or looting. The federal role will be to assist with threats to federal employees or facilities or situations that could be considered federal crimes, like organized outsiders who conspired to attack police, authorities said. The agents would only become involved if asked by local law enforcement.

The Department of Homeland Security has also sent Federal Protection Service personnel to protect federal buildings and facilities, officials said. The region is bracing for potential fallout from a grand jury decision on whether Ferguson Police Officer Darren Wilson will be charged for shooting dead Brown, 18, in that town on Aug. 9.

IN-DEPTH

— Pete Williams