If judges screen evidence, is the jury usurped?

When Bobby Lee Holmes stood trial for the rape and murder of an elderly woman in York, S.C., his defense was that someone else committed the crime. But the jury that sentenced Mr. Holmes to death never heard any of it.

The trial judge barred Holmes's lawyer from presenting evidence that someone else killed the woman and later confessed to it. Then, at the trial's end, a state prosecutor told the jury that Holmes must be the murderer because no evidence had been presented suggesting someone else might have done it.

Wednesday the Holmes case arrives at the US Supreme Court, where the justices will consider whether a South Carolina rule that lets judges prevent the accused from blaming someone else violates their constitutional right to a fair trial.

At issue is whether the US Constitution requires that a defendant be allowed to present what he or she believes to be a full defense, or whether the trial judge can exclude portions of a defendant's case from jury consideration when the judge deems the evidence unconvincing.

Holmes's lawyers say a jury should decide if a defendant's argument is convincing or not.

Lawyers for the state disagree. "The right to present evidence is not unlimited," writes Donald Zelenka, South Carolina assistant deputy attorney general, in his court brief. "Rejection of unreliable evidence does not dilute the state's burden of proof beyond a reasonable doubt."

The Holmes case arises amid increased reliance within the criminal-justice system on forensic science. Judges may be inclined to place much trust in evidence that emerges from a laboratory, experts say. But forensic specialists warn that results are only as reliable as the methods used during the investigation. In the Holmes case, the judge cited the reliability of DNA and trace fiber evidence as a reason to discount Holmes's evidence pointing to someone else as the killer. DNA evidence found on Holmes's underwear matched both Holmes and the victim.

South Carolina law forbids murder defendants from simply declaring that someone else did it. To justify presenting such a defense, a judge must find there are facts or circumstances that point to another person as the guilty party.

But weighing evidence is a function of the jury, not a judge, Holmes's lawyers say. "If a trial by jury means anything, it must mean that the jury serves as the trier of fact with exclusive responsibility for ... weighing evidence," says William Norris, in his brief on behalf of Holmes.

The Holmes defense had two parts. First, Holmes said the DNA evidence was planted by a police officer who had a grudge against him from a previous confrontation. He also had hoped to present four witnesses who heard another man confess to attacking the woman.