A New Jersey appeals court says a defendant may present expert testimony to explain how withdrawal from heroin addiction could have led him to give police a false confession.

In a published ruling, the court said withdrawal from opiate addiction is a well-recognized mental condition that could be used to explain why the defendant confessed to participating in a sexual assault and murder when there is little physical evidence linking him to the crime.

“If a defendant has a recognized, diagnosed mental condition, of a type that could make him or her more vulnerable to giving a false confession, the defense has the right to present an expert to explain the mental condition and to explain how and why it could affect the confession’s reliability,” the Appellate Division said in State v. Granskie.

Assistant Deputy Public Defender Jacqueline Turner, says the ruling is in line with prior case law that says expert testimony may be presented to explain how a person suffering from mental illness may give a false confession.

“We all know people give false confessions for many reasons,” says Turner, citing a study by the New York-based Innocence Project that estimates 25 percent of persons eventually cleared after convictions were found to have given false confessions.

“This is just a way of explaining to a jury why a person might do something like that,” Turner said. “People do it fairly often.”

Darren Gelber, the president of the Association of Criminal Defense Lawyers of New Jersey, says questions about the reliability of a confession are for a jury to decide.

“Even if the judge rules the confession was voluntary and admissible, the defendant is still permitted to argue that the statement was not voluntary or reliable,” says Gelber, of Woodbridge’s Wilentz, Goldman & Spitzer. “Expert testimony that is relevant as to reliability and voluntariness is always permitted.”

David Granskie Jr. and two other men — Rocky DiTaranto and Gary Wilson — were charged with the May 24, 2009, rape and murder of Carlyn Stone of Bridgewater, who lived with Granskie’s father. Stone was beaten to death with a cinder block.

The appeals panel upheld Somerset County Superior Court Judge John Pursel’s decision to admit Granskie’s confession, but also to allow the defense to produce an expert to discuss the effects of withdrawal on a defendant’s mental and physical state, and to explain how it could produce a false confession.

Pursel said the expert could not give an opinion as to whether the confession was reliable or unreliable.

“His ruling was consistent with settled precedent upholding a defendant’s right to present expert testimony designed to explain to the jury why a particular defendant’s psychological condition would make that defendant vulnerable to giving a false confession,” Judge Susan Reisner wrote.

“Drug addiction and withdrawal are recognized physical and psychological conditions that defendant’s expert was well qualified to explain to the jury,” she added. “Further, lay jurors might not perceive all of the ways in which a person experiencing heroin withdrawal could be vulnerable to giving a false confession.”

Expert testimony in a case like this is important because there is a paucity of physical evidence tying Granskie to the murder and assault. “The state’s case rests heavily, if not exclusively, on defendant’s confession,” said Reisner, in an opinion joined by Judges Carmen Alvarez and Mitchel Ostrer.

Wilson has pleaded guilty and is serving a 45-year sentence. Both Granskie and DiTaranto are awaiting trial.

Assistant Somerset County Prosecutor Nathan Howe, who argued the state’s case on appeal, declines to comment.