They probably know, but they don't care. All the signs are tagged with "Party for socialism and liberation". No doubt that was the organization that printed up the signs. The Marxists are always on the lookout for incidents like this that they can use to inflame racial hatred and division. It's directly out of the Marxist playbook. They use that division to sow resentment against the current system so they can eventually seek revolution, and install their own socialist system. The minorities they are using, and their allies, are nothing more than tools.
Their demands don't really make any sense. They want to do away with incarceration and prisons, but they want these cops incarcerated and imprisoned. How is that supposed to work? Since they're Marxists, I imagine they want prisons for the capitalists and current members of the system.