Prosecutors in North Carolina have strongly opposed the act since its passage in 2009, arguing that the law is far too broad, that it would be extremely costly and that it is little more than an indirect moratorium on the death penalty.

“This is not about racial justice,” said Tom Keith, a former district attorney in Forsyth County. “The real purpose is to end the death penalty, to make it so complicated and so expensive that they win by attrition.”

Supporters of the law disagreed with that reading.

“I don’t think that’s true at all,” said Tye Hunter, executive director of North Carolina’s Center for Death Penalty Litigation and one of Mr. Robinson’s lawyers. What the law does hold, he said, is that “we can’t continue to have a death penalty that depends on discrimination against African-Americans.”

The newly Republican state legislature passed a bill that would have significantly limited the scope of the law, but Gov. Bev Perdue, a Democrat, vetoed it. Republicans are planning to pass a similar law, possibly this year.

By coincidence, Friday’s decision came down two days before the 25th anniversary of the United States Supreme Court decision McCleskey vs. Kemp, in which the court ruled 5 to 4 that statistical evidence of a significant racial disparity in death sentences in Georgia was not sufficient reason to overturn a Georgia man’s death verdict. Toward the end of his decision, Justice Lewis F. Powell Jr. said that state legislatures were more qualified to decide how statistics should be used in such cases.

North Carolina’s law allows a defendant to argue that race was a significant factor in his death sentence by presenting evidence along any of three lines: that a death sentence was more likely to be sought or imposed on defendants of one race, that it was more likely when the victim was a certain race or that racial bias influenced jury selection.

Mr. Robinson is black and his victim was white — a fact that was pointed out in closing arguments by prosecutors, who described Mr. Robinson as racially biased for a violently anti-white statement he made before the murder.