
The officer, 28-year-old Darren Wilson, has left the force, citing safety concerns, according to a letter published by local media on Saturday.
A grand jury's decision on Monday not to charge Wilson in connection with the August 9 shooting death of 18-year-old Michael Brown touched off days of sporadic violence in Ferguson, a suburb of St Louis.
On Saturday, a core group of about 100 marchers, many from other states, set out on a 120-mile (192-kilometer) "Journey for Justice," heading from the St Louis suburb of Ferguson to the Missouri state capital Jefferson City.
The marchers, organized by the National Association for the Advancement of Colored People (NAACP), are demanding the sacking of the Ferguson police chief, nationwide police reforms and an end to racial profiling.
"We will fight until hell freezes over, and then we will fight on the ice," NAACP president Cornell William Brooks told supporters at Washington Metropolitan A.M.E. Zion Church before setting out. ?AFP