(AP) — Police officers and FBI agents began tearing apart a New York City basement Thursday as part of a decades-old investigation into the disappearance of 6-year-old Etan Patz, whose case made a generation of parents afraid to send their children out alone.

Etan vanished without a trace on May 25, 1979, after leaving his family’s Manhattan apartment for a short walk to catch a school bus. It was the first time his parents had let him go off to school alone.

The building being searched sits about a block from where the family lived, in the borough’s SoHo section, and is along the route that the boy would have taken on his walk to the bus stop.

Police spokesman Paul Browne said a forensic team would dig up a floor and search through the rubble for blood, clothing or human remains. The work is expected to take as many as five days.

He wouldn’t say what evidence led investigators to the property, but a law enforcement official, speaking on condition of anonymity, told The Associated Press that at the time of the boy’s disappearance, the building housed the workspace of a carpenter who was thought to have been friendly with the boy.

In the past few months, the official said, investigators had received information that Etan’s remains might be buried in the basement. Then, within the past few weeks, an FBI dog indicated the possible presence of human remains in the space, prompting the decision to dig.

The official spoke to the AP on condition of anonymity because the investigation is ongoing. Two other law enforcement officials confirmed that an FBI dog had detected the scent of remains.

Etan’s disappearance was a media sensation in 1979. The press attention helped fuel a national movement to publicise the cases of missing children. Etan’s face was among the first to appear on milk cartons. President Ronald Reagan declared May 25 National Missing Children’s Day.

Etan’s parents, Stanley and Julie Patz, became outspoken advocates for missing children. For years, they refused to change their phone number, in the hope that Etan was alive somewhere, and might call. They never moved.

Stanley Patz didn’t respond to phone calls and email messages Thursday. A man who answered the buzzer at the family’s apartment, just down the street from the building being searched, said they wouldn’t be speaking to the media.

No one has ever been prosecuted for the crime, but in recent years Stanley Patz sued an incarcerated drifter and admitted child-molester, Jose Ramos, who had been dating Etan’s baby sitter around the time he disappeared. Ramos denied killing the child, but in 2004 a Manhattan judge ruled him to be responsible for the death, largely due to his refusal to contest the case.

Ramos is scheduled to be released from prison in Pennsylvania in November, when he finishes serving most of a 20-year-sentence for abusing an 8-year-old boy. His pending freedom is one of the factors that has given new urgency to the case.

He is not the carpenter whose old workspace was being searched.

Investigators have looked at a long list of possible suspects over the years, and have excavated in other places before without success.

The 13-foot by 62-foot basement space being searched Thursday sits beneath several clothing boutiques. The building has undergone renovations over the decades, and Browne said investigators began by removing drywall partitions so they could get to brick walls that were exposed back in 1979 when the boy disappeared.

The excavation was part of a review of the case, recently ordered by the Manhattan district attorney, Browne said.

“This was a shocking case at the time and it hasn’t been resolved,” Browne said.

The law enforcement activity forced the temporary closure of some businesses on the block, including the fashion boutique Wink, on the ground floor of the excavated building.

“It’s insignificant,” owner Stephen Werther said of the lost business. “It’s retail. There’s always another day for us to make a living. This may be the family’s last chance to find out what happened to their son.”