The FBI has issued an intelligence bulletin to state and local partners urging them to be aware of the potential for violent protests after the Ferguson, Missouri grand jury issues its decision on whether or not to indict officer Darren Wilson in the shooting death of Michael Brown. That decision is expected in the next week or so.
The FBI warns that the announcement of the grand jury's decision "will likely be exploited by some individuals to justify threats and attacks against law enforcement and critical infrastructure," according to the bulletin.
The bulletin, which went out last Friday, is not based on intelligence or specific threats, but rather on "observed criminal and violent activity" in the weeks after Brown's death, a law enforcement official told CBS News' Bob Orr.
"Internet postings have called for violence against police," noted the official who told CBS News about the bulletin, calling the alert to law enforcement officers a "common sense" move taken out of an abundance of caution.
Wilson, a white police officer, shot Brown, an unarmed 18-year-old black male, in the St. Louis suburb of Ferguson on Aug. 9.
On Monday, Missouri Gov. Jay Nixon declared a state of emergency and activated the National Guard in advance of a grand jury decision, also fearing the tense street clashes between police and protesters which have manifested since the incident could rekindle, and possibly get violent.
"My hope and expectation is that peace will prevail," Nixon said. "But we have a responsibility -- I have a responsibility -- to plan for any contingencies that might arise."
There is no specific date for a decision to be revealed about whether Wilson should face charges for shooting Brown. The St. Louis County prosecutor has said he expects the grand jury to reach a decision in mid-to-late November.
New video evidence was released over the weekend in the case, adding to already heightened tensions.
New audio recordings of police radio communication before and after the teenager's shooting and video released over the weekend are helping establish a timeline of events, but they fail to answer many crucial questions about what actually occurred.
The video shows Wilson leaving the Ferguson police department hours after he shot Brown. He is seemingly uninjured -- a contradiction to what police originally said, reports CBS News correspondent Michelle Miller.
"If you got a blowout, a fracture to your eye socket, you're not just going to be walking around holding your eye," said Ben Crump, the Brown family's attorney. "We don't see him holding his eye anywhere in that video."
The encounter between Wilson and Brown took less than 90 seconds, leading to months of protests.
Police radio communications, obtained by the St. Louis Post Dispatch, shed more light on the events of Aug. 9.
"21. Put me on Canfield with two. And send me another car," Wilson could be heard saying.
Wilson first approached Michael Brown shortly after 12:02 p.m. Less than 90 seconds later, Brown was shot and another officer radioed for back-up.
"Get us several more units over here," a police officer said. "There's going to be a problem."
On Sunday, protesters braved the cold and snow on the streets of St. Louis lying down in chalk outlines of bodies and blocking traffic to commemorate 100 days since Brown's death.
"We just wanted them to know that it doesn't matter if the weather is bad, good, ugly. We'll be out here because this means that much to us," protester Rockit Ali said.
Demonstrators also targeted downtown Clayton Monday, blocking traffic at several intersections before marching to the county Justice Center. That's where the grand jury has been meeting behind closed doors since late August. No arrests were reported.
The protests are a far cry from the turmoil that shook this city and the nation only months ago, and there's fear that violence could resurface as a grand jury decides whether to indict the officer responsible for shooting the unarmed teen.