The crowd gathered at Westlake Center, then soon took to the streets in protest of King County Prosecutor Dan Satterberg's decision not to file criminal charges against Ian Birk, a former Seattle police officer.
But what started out as a peaceful protest with signs and slogans quickly boiled over as protestors clashed with police, prompting some officers to use pepper spray on the crowd.
The angry marchers smashed the back window of a police cruiser as tensions continued to escalate. The damaged patrol car, in turn, rear-ended a police van as the officer, in a hurry to get out, forgot to put the car in park.
A pedestrian in front of the van was hit, but unharmed.
The crowd, chanting, "No justice, no peace! No racist police!" marched for three hours, first to Pioneer Square before heading up to the East Precinct in Capitol Hill.
Several people threw water bottles at the police barricade that awaited them, but the crowd eventually dispersed without incident.
A number of the protestors were wearing black hoods and masks, and at least one anarchist flag was seen in the crowd. Many were carrying signs criticizing Birk and the police force.
At times they blocked traffic, testing the patience of blocked drivers.
"I cannot to this day understand why this young man has died," said Lovella Black Bear, a friend of Williams.
Friday's was the second protest of its kind in a week. On Wednesday, some 300 people gathered in protest of Satterberg's decision and peacefully marched through downtown Seattle and to the East Precinct.