A police car burns during clashes between police and protesters over the decision in the shooting death 18-year-old Michael Brown in Ferguson, Missouri, on November 24, 2014. US President Barack Obama urged calm as violent protests broke out on the streets of Ferguson after a grand jury decided a white policeman will not face charges for killing a black teen. AFP PHOTO/Jewel Samad        (Photo credit should read JEWEL SAMAD/AFP/Getty Images)