Race played a tremendous role in the American justice system during the Jim Crow era.
For the most part, this role was an informal one in that there were not laws or rules that prevented blacks from being treated equally in the justice system. For example, it was not illegal for blacks to serve on juries. However, only people who voted could serve on juries and blacks were typically prevented from voting, thus making them ineligible to serve on juries.
The major way that race affected the justice system was through the racist attitudes of the white power structure that ran the system. This can be seen in the fact that whites were willing to convict blacks of crimes on flimsy evidence as in the Scottsboro Boys' case. It can also be seen in how whites who committed violence against blacks (such as lynching or the Emmett Till case) tended to be exonerated by the justice system.
In these ways, race played a major role in the justice system in the Jim Crow era even if that role was not a formal, de jurerole.