No charges against Ferguson officer The policeman whose killing of an unarmed black teen sparked weeks of riots in the US town of Ferguson will not face charges, amid mounting anger in the streets. The tearful family of 18-year-old Michael Brown, who was shot dead on August 9, expressed profound disappointment after St Louis County prosecutor Robert McCulloch relayed the grand jury's decision. A crowd of several hundred protesters gathered in front of the police station in Ferguson where Officer Darren Wilson was based chanting: "Hey, hey, ho, ho! These killer cops have got to go. But there were no initial reports of violence, amid tight security and lines of officers in riot gear awaiting the highly-anticipated verdict. Brown's devastated mother was hugged by supporters. President Barack Obama called for calm and said the country had to accept the grand jury's decision. McCulloch told reporters the evidence presented to the grand jury had suggested Wilson had shot as a legitimate act of self-defence during a tussle that broke out as he was responding to a robbery. He said "an altercation" had broken out as Wilson was sitting in his patrol car and Brown was standing at the window. "During the altercation, two shots were fired by Officer Wilson while still inside the vehicle," McCulloch said. "Mr Brown ran east ... and Officer Wilson gave chase," he said. Mr Brown stopped and turned back toward Officer Wilson. Officer Wilson also stopped. Michael Brown moved toward Officer Wilson. Several more shots were fired by the officer and Michael Brown was fatally wounded. Having examined the physical evidence and listened to witness testimony behind closed doors, the grand jury deliberated for two days, concluding that Wilson had no case to answer. "We are profoundly disappointed that the killer of our child will not face the consequence of his actions," the Brown family said in a statement on Monday. "We respectfully ask that you please keep your protests peaceful," the family said, calling for legal reform. Answering violence with violence is not the appropriate reaction. Brown, an 18-year-old high school graduate who had planned to go to technical college, was shot at least six times by Wilson in an incident on a Ferguson street. The shooting sparked weeks of sometimes violent protests and a nationwide debate about police tactics and race relations. Before the verdict, St Louis Mayor Francis Slay admitted that "what happened to Michael Brown has deeply divided us." Ferguson's mainly African American community of 21,000 has been on edge for days, braced for further protests should the officer not be indicted. The mostly black suburb has an overwhelmingly white police force and residents complain of years of racial prejudice and heavy handed police tactics. Missouri's governor declared a state of emergency and called up the National Guard last week in readiness. The FBI has also deployed extra personnel. Shops were boarded up in Ferguson and schools in the Ferguson-Florissant District announced they would be closed Tuesday for the safety of staff and pupils.