After months of weighing evidence and testimony, a grand jury in Missouri has decided against indicting Darren Wilson, the white police officer who fatally shot unarmed black teenager Michael Brown in August.

The announcement came Monday evening after days of agonizing suspense in this central U.S. state and beyond.

“After their exhaustive review of the evidence,” jurors determined that no probable cause exists to bring charges against Wilson, said Robert P. McCullogh, St. Louis County prosecutor, speaking from the courthouse in the county seat of Clayton.

As they awaited the decision, hundreds of people gathered in the streets of nearby Ferguson, where the 18-year-old Brown was killed. The mood there was tense, with some demonstrators carrying signs bearing messages such as “Jail for Life.”

Since the August 9 shooting, demonstrations regularly have occurred in Ferguson and in Clayton, where the grand jury began meeting in late August.

On Monday, streets around the courthouse had been barricaded and neighboring businesses had boarded up storefronts, hedges against any trouble that might erupt with news of the grand jury’s decision. But, despite throngs of law enforcement officers and news media, not a protester was in sight less than an hour before McCullough shared the grand jury’s decision.

Government officials in Missouri repeatedly have appealed for calm.

At a news conference Monday evening, Governor Jay Nixon joined several other officials in calling for “peace, respect and restraint” no matter what the outcome.

“No matter what is announced, people will be emotional,” acknowledged the county’s executive, Charlie A. Dooley. He urged people “to remain focused on long-term systemic changes.” He said officials were committed to de-escalating negative actions while ensuring free speech, with the help of law enforcement and National Guard troops.

“I do not want people in this community to think they have to barricade their doors and take up arms,” Dooley cautioned.

CNN was reporting that law enforcement around the country had been put on alert, anticipating trouble if there’s no indictment.

The White House said U.S. President Barack Obama has urged any protesters to be peaceful after the decision.

Obama, speaking Sunday on ABC News’ “This Week,” said he had called Nixon “to make sure that he has a plan to respond in a careful and appropriate way to any potential violence – to be able to sort out the vast majority of peaceful protesters from the handful who are not.”

More than three months have passed since Wilson killed 18-year-old Brown after some sort of confrontation in the middle of a street in the St. Louis suburb of Ferguson.

Stories differ as to what happened August 9. Lawyers for Brown’s family say he was trying to surrender when the officer shot him. Wilson’s supporters say he shot Brown in self-defense.

The 12-member grand jury will decide whether Wilson should be charged with first- or second-degree murder or involuntary or voluntary manslaughter.

The deadly shooting sparked weeks of sometimes violent protests and looting. Police added to the tension with heavy-handed responses, including the use of armored vehicles and tear gas.

Wilson married in October

Meanwhile, St. Louis County records released Monday indicate that Wilson got married last month, The New York Times first reported. He married another Ferguson Police Department officer, Barbara Spradling, on Oct. 24. He has been on paid leave since the shooting.

The news drew a bitter response from Deray McKesson, a local activist. The Chicago Tribune reported that McKesson tweeted: “Darren Wilson is out here CHILLIN. His life clearly hasn’t slowed down even though Mike’s ended.”

Preparing for decision

Missouri Governor Jay Nixon has already declared a state of emergency and called in the National Guard in case Wilson is not indicted.

Protest groups from around the country are planning to descend on Ferguson in large numbers if the grand jury exonerates Wilson.

Law enforcement officials in Ferguson have agreed on “rules of engagement” with some organized activist groups, hoping to ensure that any demonstrations are peaceful when the grand jury decision is issued.

The father of the slain teenager appealed for calm Friday. In a video posted online, Michael Brown, Sr. said hurting others or destroying property is “not the answer” to frustration over what is seen as racial injustice.

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