CHICAGO, Nov. 24 (Xinhua/Sun) -- Darren Wilson, the white police officer of Ferguson Police Department who shot and killed unarmed Michael Brown in Ferguson, Mo., on Aug. 9, is free of indictment, the Grand Jury ruled Monday.

After an "exhaustive review" and examining the physical and scientific evidence combined with the witness statements, the grand jury concluded that Wilson is authorized to use weapons, and therefore has decided not to indict him, St. Louis County Prosecuting Attorney Robert McCulloch said.

Hundreds of people gathering outside the Ferguson police station reacted with anger and dismay when heard of no indictment for Wilson.

Shortly after the verdict, President Barack Obama made a statement, calling for peaceful protests. He said, this is a grand jury decision, "we need to accept," and "there is never an excuse for violence." He asked protesters to show restraint.

Schools in Ferguson will be cancelled on Tuesday.

The announcement of no indictment has been widely expected for weeks after multiple leaks said that there is evidence showing Brown assaulted Wilson inside his patrol SUV and tried to take his gun.

Before the grand jury's decision was announced, Missouri Governor Jay Nixon at a news conference urged all sides to "show tolerance, mutual respect and restraint" regardless of the grand jury's decision.

Consisting of three blacks and nine whites, or seven males and five females, the Grand Jury for Wilson's case convened in August. In Missouri, the grand jury does not need to be unanimous to indict, but the decision should be supported by at least nine of the 12 jury members.

The National Guard has been called in to secure critical buildings in St. Louis, including the prosecutor's office building.

It is very difficult to indict the police, senior legal analyst Jeffrey Toobin said.

Crowds of people stood on Ferguson streets waiting for the grand jury decision. Local media reported that there is a fundamental distrust of the process.

A CNN poll finds that Americans are sharply divided along racial lines as to whether Wilson should be charged with murder. Fifty-four percent of non-whites, including blacks, Latinos and Asians, say Wilson should be charged with murder, while just 23 percent of whites agree.

Thirty eight percent of whites say Wilson should not be charged, while just 15 percent of non-whites hold the same opinion. But most Americans agree that Wilson should at least face some form of criminal charges, the poll finds.

Witnesses and police have conflicting accounts of Brown's death. Police said Brown struggled with Wilson inside his police car and reached for Wilson's weapon, while Brown's family and some witnesses said Wilson killed Brown as he raised his hands in surrender.

This is the most controversial case in the United States, CNN said.

To prepare for possible unrest or violence, Missouri Governor Jay Nixon declared a state of emergency on Nov. 18 and activated the National Guard as a precaution.

U.S. Attorney General Eric Holder on Nov. 21 urged law enforcement officers and protesters to keep calm. Holder encouraged law enforcement officials in every jurisdiction to work with the communities that they serve to minimize needless confrontation.

To protesters, Holder said, "History has shown us that the most successful and enduring movements for change are those that adhere to nonaggression and nonviolence."

He asked those who seek to lend their voice to important causes and discussions and those who seek to elevate these vital conversations to do so in a way that respects the gravity of their subject matter.

Brown's father on Nov. 20 also called for calm ahead of the decision from a St. Louis County grand jury, saying "No matter what the grand jury decides, I do not want my son's death to be in vain - I want it to lead to positive change."

Unarmed 18-year-old Michael Brown was shot dead by white police officer Darren Wilson in Ferguson, Mo., on Aug. 9. The shooting led to weeks of protests and saw citizens and heavily armed police clash. Hundreds were arrested.