The grand jury considering whether to indict the Ferguson police officer who shot and killed teenager Michael Brown is unlikely to meet and render a decision this weekend, sources told Fox News on Saturday.

Those same sources say it is likely the grand jury will wait until Monday to reconvene.

The 12-member grand jury has been considering whether charges are warranted against Officer Darren Wilson, who shot and killed the 18-year-old Brown on Aug. 9 during a confrontation on a street in Ferguson. Wilson is white and Brown, who was unarmed, is black.

There have been many demonstrations in the months since Brown's death, including some that were violent. Police arrested three protesters on Friday night -- the third straight night of unrest in the St. Louis area.

The FBI confirmed Saturday that they had arrested two men accused of buying explosives, that they reportedly planned to use in protests in the area.

On Saturday, the authorities set up barricades around the Buzz Westfall Justice Center in Clayton, which is where the grand jury has been meeting.

Barricades also went up in the shopping center parking lot on West Florissant Avenue in Ferguson, which was where police set up a makeshift command center in the immediate aftermath of Brown's death.

Several businesses in both Ferguson and Clayton have put boards on their windows.

Residents were on edge, too.

Jamie Freeman of Ferguson, 38, a registered nurse and mother of four, said she was especially concerned since her 20-year-old son lives in the neighborhood where Brown was shot.

"I just hope it stays peaceful," Freeman said of protests that will follow the grand jury decision. "We all have human emotions, bit there's a way to do things, and violence, you can't get peace from violence."

Crump, the Brown family attorney, seemed doubtful that Wilson would be charged, saying the grand jury process is weighted against those shot by police officers.

"Ninety-nine percent of the time the police officer is not held accountable for killing a young black boy," Crump said. "The police officer gets all the consideration."

The FBI has sent nearly 100 additional agents to Ferguson to help law enforcement agencies, according to a U.S. official who spoke on condition of anonymity because the official was not authorized to discuss the FBI plans.

The Associated Press contributed to this report.