Racial Discrimination in Jury selection.

The issue of racial discrimination in criminal trials is again getting attention.  Having been both a defense attorney and prosecutor I can tell you that neither side uses its peremptory challenges directly to insure an unbiased jury.  Challenges are used to  get rid of anyone who might be biased in favor of the other side. Prosecutor's often fear that black jurors are more likely to identify with the defendant or have had bad experiences with the police. The theory is that the net result is an unbiased jury.  This doesn't always work.  
According to the Dallas Morning News:

"Racial discrimination during jury selection plagued the Dallas County district attorney’s office for years, The Dallas Morning News reported during a series of stories in March 1986. The U.S. Supreme Court cited The News’ work in a 1986 decision, Batson vs. Kentucky.
The News reported that a 1963 treatise by a Dallas County prosecutor recommended against permitting “Jews, Negroes, Dagos and Mexicans or a member of any minority race on a jury, no matter how rich or how well educated.”

Racial discrimination during jury selection plagued the Dallas County district attorney’s office for years, The Dallas Morning News reported during a series of stories in March 1986. The U.S. Supreme Court cited The News’ work in a 1986 decision, Batson vs. Kentucky.
The News reported that a 1963 treatise by a Dallas County prosecutor recommended against permitting “Jews, Negroes, Dagos and Mexicans or a member of any minority race on a jury, no matter how rich or how well educated.”

Remember, however, not every strike of a black juror is motivated by prejudice.  There are often neutral reasons (e.g., is a neighbor of the defendant).