A confidential informant used by Prince George's County police on several drug cases should have been named during trial, the state's highest court ruled in a blow to the secretive arrangement used by authorities to make arrests. The Maryland Court of Appeals overturned the conviction of Winston Elliott, who was arrested in 2006 in a Prince George's County parking lot with 20 pounds of marijuana in his vehicle. The arrest was made after a tip from a police source who previously provided "accurate, proven and corroborated" information that led to the seizure of "large quantities" of marijuana, according to court documents.

However, the appeals court ruled that Elliott's defense was hampered by an inability to question the source during trial. Elliott argued that the police source, in fact, had provided him with the drugs, but prosecutors were never forced to disclose the identity of their source to the jury.

"Although Maryland recognizes the privilege of the state to protect the identity of informants, the privilege is limited by the defendant's interest in a fair trial," the court's opinion reads. "The court must properly balance the public's interest in protecting the flow of information against the individual's right to prepare his defense. Elliott's right to prepare his defense would outweigh the public interest in protecting the flow of information."

The judges said that cases involving entrapment and mistaken identity have historically warranted the identification of tipsters.

Elliott's case now returns to county circuit court -- and taxpayers will foot the bill for Elliott's multiple appeals of his guilty verdict.

However, county officials say they will continue to rely on confidential sources and push to keep them private.

"This is not a question of the state hiding the ball," said Ramon Korionoff, spokesman for the Prince George's County state's attorney, calling the use of private informants "common practice."

The informant in question was previously involved in buying and selling drugs, but police agreed not to arrest him in exchange for future cooperation with investigations, court documents show.