“I watched the video a couple of times and I was just in disbelief that that was actually happening, or that it actually happened,” Welch said. “To see that officer’s knee on his neck as he basically pled for his life, and the officer completely indifferent, was just unbelievable. I mean, I was really left speechless by the disbelief.”

But that video was just one of the latest in a long succession of such killings of unarmed people of color, reminding people of Trayvon Martin, a Florida teenager shot and killed by a neighborhood watch captain in 2012; Michael Brown, the black teenager whose shooting death by police sparked riots in Ferguson, Mo., in 2004; and Breonna Taylor, a 26-year-old emergency medical technician who was shot and killed by police in her own home in Louisville, Kentucky in March of this year.

Together, those deaths and many others have exposed the extent to which African Americans and other people of color are treated differently by law enforcement agencies, the result, many say, of a pattern of systemic racism that has existed in America for more than four centuries.

All four officers involved in Floyd’s death have since been fired. One is charged with second-degree murder while the other three are charged with aiding and abetting in the crime.

But even that has not been enough to quiet the anger of people who have taken to the streets, including the streets of Chicago and its surrounding suburbs, where peaceful protests last week escalated into violence and looting.