NEW YORK - Investigators ripped up the basement floor of a Manhattan building Friday in a hunt for the remains of a 6-year-old boy who disappeared on his way to school in 1979.

Utility workers with jackhammers and saws helped chip away an area around aging pipes, then law enforcers wearing workmen's gloves carried out the basketball-size chunks of rubble and carefully placed them in refuse bins. The material will be sifted and then taken elsewhere for testing.

Etan's disappearance on May 25, 1979, drew national attention to child safety, ushered in a generation of parents who became afraid to send their kids out alone and helped fuel a movement to publicize missing children's cases. President Ronald Reagan declared the day of the boy's disappearance National Missing Children's Day.

The space being escavated was about a block from the bus stop where Etan was headed when he vanished. It is one of the few secluded places, easily accessible from the street, that sat along his two-block walk to the bus from his home.

At the time, part of the basement was being used as a workshop by Othniel Miller, a neighbourhood handyman who had been friendly with the family.

Police and FBI officials haven't named a suspect in the case.

Miller, now 75 and living in Brooklyn, hasn't spoken publicly about the investigation. His lawyer, Michael Farkas, told journalists gathered outside Miller's home his client was co-operating with investigators and had "no involvement in this tragic event."

The renewed investigation recalls the years when printed images of missing children appeared on milk cartons.

"The story really resonated and touched millions of moms and dads," said Ernie Allen, the president of the National Center for Exploited and Missing Children. Etan's face appeared on milk cartons, and the boy's thick blond locks and goofy grin tugged at the public's heartstrings.

"What it did was raise the level of awareness," said Noreen Gosch, whose missing son, Johnny, was among the first used in the now-abandoned milk carton campaign. "It didn't necessarily bring us tips or leads we could actually use."

Her son, who disappeared on his newspaper route in West Des Moines, Iowa, in 1982, has never been found. His image appeared on milk cartons probably in 1983, Gosch said. The milk carton campaigns faded away beginning in the late 1980s after pediatricians, including Dr. Benjamin Spock, criticized the images for inducing unwarranted fear in children as they ate breakfast.

The FBI and New York City police have spent 33 years trying to find out what happened to Etan, without success.

Police Commissioner Raymond Kelly confirmed Friday that investigators made the decision to dig after an FBI dog detected the scent of human remains in the basement space.

"The investigation 33 years ago actually led them to that location. They spoke to people in that building. It's along the route that Etan took to leave his house and go into the bus, so it's a logical place to look," Kelly said.

FBI spokesman Tim Flannelly said it was "one lead of many."

"We're out here 33 years after his disappearance, and we're not going to stop," he said.

Miller has been interviewed by investigators several times over the years. He was questioned again recently, and as a result of those discussions, they decided to refocus their attention on the building, according to a law enforcement official. The official spoke to the AP on condition of anonymity because the investigation is ongoing.

Etan's parents, Stanley and Julie Patz, still live in the apartment they had when he disappeared.

A sign taped near their door buzzer Friday read: "To the hardworking and patient media people, the answer to all your questions at this time is no comment. Please stop ringing our bell and calling our phone for interviews."

The family, and some investigators who had previously worked on the case, had long believed that the person responsible for the boy's death was Jose Ramos, an incarcerated pedophile who knew a woman who briefly worked as one of Etan's caretakers.

Ramos, now serving the final months of a prison sentence for abusing an 8-year-old boy in Pennsylvania, has denied killing the child. His pending freedom is one of the factors that caused investigators to renew their effort to solve the case.

The Patz family sued Ramos in civil court, and won a judgment against him in 2004, largely because he declined to participate in the litigation.