These weren’t isolated events. A 2012 report from University of Missouri–St. Louis criminologist David Klinger found that, from 2008 to 2011, St. Louis police officers fired their weapons 98 times. “Any comparison across cities right now is still missing the lion’s share of circumstances in which people are shot by the police,” Klinger said to the St. Louis Post-Dispatch. “There are only a smattering of cities that report their officer-involved shootings, and when compared against them, St. Louis is on the high end.” The data on police violence is incomplete, as there is no federal effort to pull together information on unjustified homicides.
...But the St. Louis area PD seem highly dysfunctional (putting it mildly), in light of increasing evidence.
Like many American cities, St. Louis can’t be untangled from segregation. In 1916, it became one of the first places to formalize racial segregation by designating particular “Negro blocks” where blacks would be concentrated and legally forbidden from leaving. The Supreme Court struck the ordinance in 1917, but private real estate agents and other groups responded with informal means of enforcing segregation. In 1923, the St. Louis Real Estate Exchange created zones in the city’s black neighborhoods to limit the extent of black housing. Real estate agents could sell to black families inside the zones, but would lose their licenses if they sold homes outside the zones.
The list of nefarious anti-black schemes continues through the decades. That's the background for the story. Even if that were not the case, this community is behaving extraordinarily peacefully; they have every right to be angry, let alone exercise their right to assemble.