Five main reasons that people of color are overrepresented in the United States criminal justice system may be the general over-policing of racial minorities, over-policing of marginalized communities, specific discrimination in the implementation of stop and search policies, biased use of discretion by prosecutors, and policies that disadvantage people of color.
Attached below is a report to the United Nations on racial disparities in the United States criminal justice system compiled by the Sentencing Project, an advocacy group based in Washington, DC. The report argues that racial minorities receive a disproportionate amount of police attention in general terms and specifically in the use of stop and search procedures. The same is true of the poor and marginalized communities in which people of color are disproportionately represented.
In addition to these problems of policing, prosecutors are more likely to charge people of color with offenses that carry a mandatory minimum sentence than they are to charge white people with these offenses. Also, laws such as those which provide for enhanced sentences for offenders selling drugs in school zones disproportionately affect residents of high-density urban areas. People of color are overrepresented in these areas and therefore more likely to be subject to these longer sentences.