Who caused the violence at the March?

On Page 161, we learn that a local store owner had to close his doors because he was robbed by some of the marchers. We also learn that the police and some of the young men were battling in the alleys.... that boys were throwing bottles at swuqad car windows. In essence, the answer to this question requires your opinion. Who was at fault? Was the protest peaceful? Why did the police step in?