By Joseph Ax

NEW YORK, Feb 22 (Reuters) - When is a confession not enough?

That question is at the heart of the case against Pedro Hernandez, who was indicted after confessing last May to the notorious 1979 kidnapping and murder of 6-year-old Etan Patz in New York.

Hernandez's lawyer, Harvey Fishbein, has cited a rarely invoked New York law to argue that Hernandez's confession alone is not legally sufficient to support the charges.

That could be an uphill climb, given how liberally New York courts have interpreted the law, according to more than half a dozen law professors, defense lawyers and former prosecutors interviewed by Reuters.

Under sections 60.50 and 190.65 of New York's criminal procedure laws, a confession alone cannot form the basis of an indictment. Instead, prosecutors must furnish "additional proof that the offense charged has been committed."

In several key rulings, New York's highest court has found that the requirement is a low bar to clear. The Patz case could be a crucial test of whether the law has any teeth left.

Steve Zeidman, a law professor at the City University of New York, said it represents a chance, however slim, for the pendulum to swing in the other direction.

"You would think that given all we know about false confessions ... courts would interpret these laws more strictly," he said. "This case could help make it happen."

Patz vanished from a Manhattan street on his way to school, leaving behind no evidence, no body and no witnesses in one of the city's most notorious unsolved crimes.

More than 30 years later, Hernandez, 51, who worked at a deli near the Patz home at the time, told police he strangled the boy in the store's basement and dumped the body in the trash.

Fishbein argues that Patz's disappearance alone doesn't satisfy the law's requirement for "additional proof." He also claims that Hernandez's confession was prompted by mental illness.

"There is no evidence of anything other than the fact that Etan Patz is missing," he wrote in a motion requesting a copy of the grand jury minutes, a preliminary move before seeking a dismissal of the charges.

Prosecutors countered in a reply motion that they have provided enough evidence to satisfy the law.

'VERY LITTLE EVIDENCE' REQUIRED

The two statutes Fishbein is citing have not often been put to the test because for most crimes there is physical evidence left behind. When asked to consider the issue, the Court of Appeals has previously found that little evidence of any kind is needed to meet the requirement of "additional proof."

In the 1975 case People v. Daniels, the court held that the only evidence needed to corroborate a confession is "some proof, of whatever weight," that the crime had occurred. The court has said in other rulings that the evidence also doesn't need to link the confessor to the crime.

The Manhattan district attorney's office declined to comment on what evidence prosecutors believe corroborates Hernandez's confession.

They suggested, in court papers responding to Fishbein's grand jury motion, that Patz's sudden disappearance would be enough on its own to satisfy the statutes, which they said require "very little evidence."

The court papers claimed Fishbein's own motion listed "factors, from information that is publicly available," that would serve to meet the statutory requirement.

"For example, it is widely known that Etan Patz left his home on the morning of May 25, 1979, to walk to his school bus stop near the corner of West Broadway and Prince Street and has never been seen or heard from since that date," prosecutors wrote.

Pace University law professor Bennett Gershman, a former prosecutor, said a grand jury should be able to make reasonable inferences based on the circumstances of Patz's disappearance.

"This little boy was walking to the bus and never got there," he said. "It's logical to infer that he was abducted and killed."

University of Michigan law professor Steve Moran, who has studied confession corroboration laws across the country, said he would be "shocked" if Fishbein's argument swayed a judge into tossing the indictment.

But Steven Banks, the attorney-in-chief for the Legal Aid Society, said if courts accept that an unexplained disappearance is enough to corroborate a murder confession, it will render the statute meaningless.

LOWERING THE STANDARD

Corroboration statutes stem from a common law concept, corpus delicti, which requires that prosecutors show a crime occurred before securing a conviction. In homicide cases, the rule prevents a situation where a supposed murder victim later turns up unharmed.

According to Moran, the co-founder of the Michigan Innocence Project, the standard has been steadily weakened since a 1954 U.S. Supreme Court case, Opper v. U.S.

In Opper the court held that evidence corroborating a confession does not have to establish that the crime occurred but must only "tend to establish the trustworthiness of the statement" in federal cases. Many states have since followed suit, Moran said.

"That's really no rule at all," he said. "The point of having a robust corroboration rule is that people sometimes confess to crimes that either did not occur at all or they didn't commit, and that juries have an exceptionally hard time recognizing that fact."

Manhattan Acting Supreme Court Justice Maxwell Wiley has said he will rule on Fishbein's request for the grand jury minutes next month. Fishbein said he plans to file a motion to dismiss once Wiley has ruled.

Follow us on Twitter @ReutersLegal | Like us on Facebook