ANNAPOLIS, Md. (AP) _ An appeals court Tuesday overturned a death row inmate's conviction for shooting two prominent Washington lawyers in the back of the head, citing trial errors prejudicial to the defense.

The Court of Appeals said the trial judge should have allowed Scotland Williams' defense lawyers to question a laboratory employee about its past DNA test practices.

The court also reversed a burglary conviction against Williams, saying the judge should not have allowed a crow bar used in the burglary into evidence.

Williams was convicted in March 1995 of the murders of Jose Trias and his wife, Julie Gilbert, who were shot during the burglary as they lay in bed in their weekend home near Annapolis.

At the time, Williams was 31 and unemployed after being honorably discharged from the Army. Arrested after he was identified from videotapes taken as he used the couple's bank card at automatic teller machines, Williams denied killing the couple and said he found the card.

One of the key pieces of evidence was DNA taken from a glass in the home that Cellmark Diagnostics Inc. said matched Williams' DNA. The Germantown-based Cellmark also examined evidence in the O.J. Simpson trial.

The appellate panel said Judge Eugene Lerner should have allowed defense lawyers to question a Cellmark employee about mistakes other technicians had made in carrying out tests of DNA samples in other cases.

Tuesday's ruling reverses the conviction and death sentence.

Prosecutor Cynthia Ferris strongly criticized the court's ruling and said Williams will be tried again.

``We'll retry it as many times as it takes because he is clearly guilty. It was a heinous crime, two very fine people were basically executed,'' Ms. Ferris said.

Michael R. Barudes, an assistant public defender who worked on Williams' appeal, said he had not seen the opinion and couldn't comment on it.

Trias, 49, the son of a former Puerto Rican Supreme Court justice, was chief counsel for the Howard Hughes Medical Institute in Chevy Chase, one of the nation's largest philanthropies. Ms. Gilbert, 48, was a partner in the Washington law firm.