A STRANGELY divided Supreme Court on Tuesday held that a jury must be unanimous -- really unanimous -- before it can convict somebody, even a drug kingpin. The six-vote majority included the court's right flank -- Chief Justice William Rehnquist, and Justices Clarence Thomas and Antonin Scalia -- along with the more liberal Justices John Paul Stevens, David Souter and Stephen Breyer, who wrote the opinion. Dissenting were Justices Sandra Day O'Connor and Anthony Kennedy, who are more typically swing votes, along with Ruth Bader Ginsburg.

The court held in essence that when the government accuses someone of "engaging in a continuing criminal enterprise," which requires proving that the accused directed a series of violations of the drug laws, it must do more than convince a jury that such a series of violations existed. Wrote Justice Breyer, the jury "must unanimously agree not only that the defendant committed some `continuing series of violations' but also that the defendant committed each of the individual `violations' necessary to make up that `continuing series.' "

The question at issue in this case masks an important principle: that it is the government's obligation to prove every component of the crime alleged with enough specificity that the jury convicting a defendant is unanimous about his conduct. As Justice Scalia once pithily wrote, "We would not permit . . . an indictment charging that the defendant assaulted either X on Tuesday or Y on Wednesday." If someone is to be locked up for a long period of time, there can be no question about whether the jury knew what it was doing.

The law at issue mandates stiff sentences for violations of the drug laws by people at the helms of organizations that are involved in a "continuing series" of other drug violations. It can easily be read to erode the principle of jury unanimity. Lower courts had held that it was not essential for the jury to agree on which specific violations constituted the continuing series, as long as it agreed that the defendant had committed at least three. But as Justice Breyer correctly argued, reading the statute that way could "cover-up wide disagreement among the jurors about just what the defendant did, or did not, do."

Justice Breyer's decision is both rigorous and right, though perhaps inconvenient for prosecutors in cases that are indisputably important to antidrug and organized crime efforts. But it is not too much to ask for prosecutors to convince the whole of a jury of the same set of facts. It seems only fair.