Police in the United States are generally permitted to use lethal force when the situation requires it. In other words, they may need to use lethal force to protect their own lives or the lives of others. In other circumstances, police need to use other less violent means to enforce the law.
There is no reason that someone meant to protect and serve should hurt an innocent person. Police officers should focus on helping all people, not just people of a certain background. This is certainly a problem in Chicago as well as surrounding areas, but there is some good news.
There are a number of fatal shootings of black people by police within the United States in the media presently. The problem with this can't be understated, but there is an issue. There is very little information on how racial bias impacts fatal police shootings, and because of that, it's complicated to define the true impact race has on law enforcement.
We can find case after case of police brutality in Chicago's law enforcement records and judicial proceedings. Perhaps your experience was similar to one victim who claims two officers slammed her against a building, pulled her hair and pushed her to the ground.