There was a major break Thursday in one of the most high-profile missing child cases in U.S. history, when a man told police that he killed six-year-old Etan Patz in 1979.

Pedro Hernandez, a former New York City convenience store clerk, told investigators that he suffocated Etan, and later dumped the body in an alleyway.

Etan disappeared on his way to school and helped spark the nation's missing children movement.

It's not clear if Hernandez's story checks out, but if it does, it could mark the final chapter in a long-running murder mystery that has puzzled investigators and the public alike.

Still, officials reminded the public that the confession from Hernandez, believed to be in his 60s, means nothing until details are confirmed.

"Let me caution you that there's still a lot of investigating to do," New York City Mayor Michael Bloomberg said Thursday.

But it is known that Hernandez worked at a store in the same area where Patz lived in 1979.

An official who spoke on the condition of anonymity told The Associated Press that Hernandez admitted to suffocating the child, putting his body in a box, walking down a Manhattan street and then leaving the box in an alley.

Etan vanished as he walked alone to a bus stop, only two blocks from his home in the bustling SoHo neighbourhood. Three decades ago, it was a working-class area and didn't much resemble the gentrified version of today's SoHo. Etan and his parents had just moved to the area.

The admission of guilt comes a day before the anniversary of Etan's disappearance -- a day when investigators are often sorting through numerous phony confessions and hoaxes.

Hernandez, who now lives in New Jersey and moved there shortly after Etan vanished, was picked up by police on Wednesday and questioned the next day at the district attorney's office in Manhattan.

In fact, Hernandez had been tied to the case in the past and police recently got a phone call with a fresh lead, officials said. However, they would not comment specifically on the nature of the tip.

But for the people who know Hernandez, his confession is bizarre.

"I can't believe something like that," said neighbour Dan Wollick, who lives in the same apartment building.

"This guy, he doesn't seem that way."

Others say that Hernandez lives with his wife and has a daughter who goes to university.

The FBI has not commented publicly on the case, and Etan's parents have not spoken out about the recent developments.

But New York Police Commissioner Raymond Kelly stated that a male "made statements to NYPD detectives implicating himself in the disappearance and death of Etan Patz."

The investigation, which ushered in a new era of caution for parents in many cities across North America, has had leads before.

In fact, past efforts had concentrated on a convicted child molester named Jose Ramos, who had been dating Etan's babysitter at the time of his disappearance.

But those leads turned up empty, and Etan's father had his son declared legally dead in 2001 so he could sue Ramos.

In 2004, a judge ruled in a civil case that Ramos was responsible for the boy's death after he refused to answer questions. But no criminal charges were ever laid.