Ferguson, Mo. (CNN) -- A Missouri grand jury has decided not to indict Ferguson police officer Darren Wilson in the Aug. 9 shooting death of Michael Brown, St. Louis County Prosecuting Attorney Robert McCulloch said Monday night.
After an "exhaustive review," the jurors deliberated for two days, he said. The grand jurors are "the only ones who have heard all the evidence," McCulloch said.
Brown's father is "devastated" that Wilson will not face charges, a spokeswoman for Michael Brown Sr. told CNN's Evan Perez.
"While we understand that many others share our pain, we ask that you channel your frustration in ways that will make a positive change. We need to work together to fix the system that allowed this to happen," the family said in a statement.
President Barack Obama echoed the words of Michael Brown's father, calling for the Brown's death to lead to "incredible change, positive change" and for people not to hurt others or destroy property.
It is an "understandable reaction" that some Americans will agree and others will be made angry by the decision to not indict Officer Darren Wilson, Obama said Monday night.
"First and foremost, we are a nation built on the rule of law, so we need to accept this decision was the grand jury's to make," he said.
Hundreds of people gathered outside the Ferguson police station reacted with anger and dismay as word spread that there would be no indictment.
Some people broke down in tears. Others threw their hands up and screamed. A chant arose, " F*ck the police! "
The crowd surged toward the metal gates in front of the station and were met by officers in full riot gear. Another chant arose: "No justice, no peace!"
Some protesters destroyed a police car, and one demonstrator was seen dousing another patrol car with lighter fluid before police in riot gear moved in, CNN correspondent Jason Carroll said.
At least one gunshot was heard near the Ferguson Police Department, CNN's Sara Sidner said.
And some protesters were seen throwing bottles at police.
While protesters chanted late Monday for an indictment in the shooting death of Michael Brown, officials called for calm as the world awaits word of the grand jury's decision.
"No matter what is announced, people will be emotional. I want people to think with their heads and not with emotion," said St. Louis County Executive Charlie Dooley. "This is not the time to turn on each other. It is a time to turn to each other."
Protesters were gathering outside the police department in Ferguson. Darren Wilson, a white police officer with the department, shot and killed Brown, a black teenager, on August 9.
State and federal sources told CNN the grand jury decision will be announced some time Monday. The prosecutor's office formally announced that a decision has been reached, but the news of the actual decision will come later in the day.
People in this St. Louis suburb have been waiting since August 9, when Brown, 18, was fatally shot by Wilson.
The killing restarted a national debate on race and law enforcement. Nowhere was the tension more evident in the predominantly black town of Ferguson, which has a mostly white police department and town government. Brown was black, Wilson is white.
Supporters of Brown's family back witness accounts that Wilson fired while Brown had his hands up in surrender. Wilson's supporters say that Brown was the aggressor and had tried to take Wilson's gun while he was in his vehicle and that the officer fired in self-defense.
The town couldn't even agree what happened during weeks of street demonstrations. Protesters argued that authorities were trying to stifle protests; officials said they were acting to keep violence under control.
'We're just ready for it to be over with'
The city has been on edge in anticipation of a decision, and activists are prepared to protest. Brown's family has been notified of the decision, an attorney told CNN. Law enforcement sources said the grand jury has been sent home.
"We're prepared for any decision that comes down," Missouri Public Safety Director Daniel Isom told CNN.
More businesses boarded up, but streets were quiet in the afternoon as residents waited.
Byron Conley, protesting outside city police department, told CNN's Sara Sidner, "We're just ready for it to be over with. Let's get on with our lives."
Rick Canamore stood with his sign -- "RIP Mike Brown" -- outside the police department.
If the grand jury does not indict Wilson, anger is sure to consume people such as Canamore.
"I'm already angry because it has taken so long," he said. "If Mike Brown had shot Darren Wilson, it would have been over a long time ago. But Darren Wilson is walking around free. He hasn't apologized to Mike Brown's family. He has not apologized to the community."
Though the basic facts of the case -- that Brown was unarmed when Wilson shot him -- are not in question, the facts of the fatal moment are hotly disputed.
Unanimous indictment decision isn't needed
Unlike a jury in a criminal case, which convicts someone if jurors are convinced of guilt "beyond a reasonable doubt," a grand jury decides whether there is "probable cause" to charge someone with a crime, based on testimony and evidence presented.
In Missouri, grand jurors don't have to be unanimous to indict, as long as nine of the 12 agree on a charge.
The grand jury can issue an indictment on any of those four charges. It also can add a charge of armed criminal action, authorities said.
But the grand jury, which received the Missouri statutes for self-defense and the police use of deadly force, may choose not to indict Wilson.
The grand jury meets in secrecy and first met in August. While the jury members are not identified, authorities have released some information about them.
The group of 12 includes nine white people (six men and three women) and three black people (two women and one man), court officials said.
The county grand jury was randomly selected from an approved pool and has been seated since May, according Paul Fox, the director of judicial administration for the St. Louis County Circuit Court.
Many grand juries hear numerous cases. These juries last for a specified period of time rather than the duration of a specific case.
Wilson himself testified before the grand jury, CNN legal analyst Jeffrey Toobin said, an unusual move because he gave up his Fifth Amendment rights in doing so.