CAMBRIDGE, Mass. — NEARLY 50 years after the end of Jim Crow, African-Americans are still facing execution because of their race.

Duane Buck could end up being one of them. He was convicted in 1997 of the murders of two people in Harris County, Tex., home to the city of Houston. He does not deny his guilt in these terrible crimes, so there is no question that he must be punished. But what happened at Mr. Buck’s sentencing hearing is appalling, even for Texas, which was once among the handful of states that led the country in the lynching of African-American men and which is now the country’s most prolific executioner.

During the presentation of evidence at the penalty phase of Mr. Buck’s trial — when the jury was required to decide between the death penalty and a life sentence — the trial prosecutor elicited testimony from a psychologist for the defense indicating that Mr. Buck’s race made him more likely to be violent in the future.

The prosecutor asked, “You have determined that the sex factor, that a male is more violent than a female because that’s just the way it is, and that the race factor, black, increases the future dangerousness for various complicated reasons; is that correct?”