One prospective juror did not make enough eye contact. Another appeared nervous and confused. A third had a son who was close in age to the defendant. A fourth was involved with the Head Start program.

These were just a few of the dozens of reasons Georgia prosecutors gave for eliminating people from sitting on the jury in the 1987 murder trial of Timothy Tyrone Foster, an 18-year-old black man charged with killing a 79-year-old white woman named Queen Madge White.

The one reason prosecutors did not give was the one thing those four potential jurors had in common: They were black.

A year before Mr. Foster’s trial, the Supreme Court, in the case of Batson v. Kentucky, reaffirmed that it is unconstitutional to exclude jurors because of their race — a practice with a long, odious history. It has survived thanks to the so-called peremptory challenge, which allows a juror to be excluded for no reason at all, as opposed to “for cause” challenges, in which a lawyer must give a reason for an exclusion, which the judge can accept or deny.