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In addition to the FBI, other federal agencies have also mobilized staffers to get to St. Louis today, sources told ABC News.
A decision by the grand jury is expected soon, but St. Louis authorities said today that the grand jury is still meeting. The panel will decide whether or not to indict Ferguson Police Officer Darren Wilson for shooting Brown, who was unarmed, on Aug. 9.
Authorities are braced for a recurrence of angry protests that turned violent at times during the summer.
The FBI has ordered its Ferguson contingent to mobilize and arrive in the St. Louis area today. In addition to FBI personnel already in the St. Louis area, about 100 more are being dispatched, law enforcement sources said. Additional FBI personnel have been put on alert so that they could be called in as part of a second emergency wave if necessary, ABC News has learned.
The FBI is opening up its special St. Louis intelligence center today. This facility will be in constant contact with the Missouri and St. Louis County Emergency Operations Center.
The FBI declined to comment.
Missouri Gov. Jay Nixon declared a state of emergency earlier this week and activated the Missouri National Guard to help keep order if necessary.
Michael Brown Sr., the father of the slain teen, issued a videotaped appeal this week for protester to remain peaceful whatever the verdict.