By Natasja Sheriff

NEW YORK (Reuters) - The murder trial of a former deli worker who confessed to strangling 6-year-old Etan Patz resumed on Friday with the 18th day of jury deliberations.

The panel at state Supreme Court in Manhattan has been struggling to reach consensus on the kidnapping and murder charges against Pedro Hernandez. Since deliberations began on April 15, the panel has deadlocked twice but was directed by Judge Maxwell Wiley to keep trying.

Patz's disappearance more than three decades ago brought national attention to the issue of abducted children and changed the way the United States responds to reports of missing kids. His picture was one of the first to appear on milk cartons in a campaign to locate abducted children.

Patz vanished on May 25, 1979, as he walked alone for the first time to a school bus stop in his Soho neighborhood in Manhattan. The crime long haunted New Yorkers who can recall the massive search for the missing blond boy, who was never found. He was declared dead in 2001.

Hernandez, 54, confessed to police in 2012 that he lured the boy with the promise of a soda, choked him in the basement of the deli, stuffed him in a box and left the boy's still-moving body in an alley.

But Hernandez's attorneys argued that he is mentally ill and that police coerced his confession.

They say the real culprit is a longtime suspect, Jose Ramos, whose girlfriend walked Patz home from school. Ramos, convicted of sexually abusing boys, is serving a prison term in Pennsylvania.

Prosecutors say Hernandez is a cunning criminal whose confession was voluntary.

The marathon jury deliberations were the longest in recent memory, said David Bookstaver, a spokesman for the state Office of Court Administration. The agency does not keep records on the length of jury deliberations.

There is no limit to the number of times the judge could send the jury back to deliberate, but at some point such instructions would be considered coercive by an appeals court, said Alice Fontier, one of the defense attorneys.

If a mistrial is declared, the prosecution will have to decide whether to retry the case.

(Editing by Barbara Goldberg and Doina Chiacu)