(CBS/AP) NEW YORK - FBI agents and New York City police officers were in a downtown New York City basement Thursday, searching for clues in the 1979 disappearance of Etan Patz.
CBS New York reports authorities have previously searched the building at Prince and Wooster streets where Patz lived.
Patz vanished without a trace in May 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 they searched on Thursday is about a block and a half away and on the same route Patz would have walked to the school bus.
Police spokesman Paul Browne said a forensic team was looking for blood, clothing or human remains. They are expected to be at the site for as many as five days. He wouldn't say what evidence led investigators to the property.
"The FBI and the NYPD are looking for evidence in the Etan Patz investigation. It's one of many leads that we're pursuing. It is a joint matter between the FBI and NYPD and no conclusions should be made about specifically why we're here or what we're looking for," FBI spokesman Tim Flannley.
Investigators will also be taking down dry wall, possibly a brick wall, excavating the concrete floor and sifting through it.
According to CBS New York, a new search warrant was issued in the last week, allowing this search to begin Thursday.
Reports say handyman, who worked in the building where police are searching, knew Patz and occasionally gave him $1 to help him do some work. Around the time of Patz's disappearance, that handyman put down a new concrete floor in the basement of the building. That floor has allegedly never been broken up until now.
District Attorney Cy Vance confirmed in May, 2010 that his office would reopen the case. "This was a shocking case at the time and it hasn't been resolved," Browne said.
Patz's disappearance caused a frenzy in New York City. It also prompted huge changes in the way missing child cases were handled. Patz was the first missing child to appear on the back of a milk carton.
"We obviously are looking to bring closure to the investigation and to the family but that'll be determined throughout the course of this case," Flannley said. "We are obviously optimistic that we might find evidence but again people shouldn't draw conclusions from this. We're doing the best we can to bring closure in this matter."
No one has ever been prosecuted for the crime but the boy's parents sued an incarcerated drifter and admitted child-molester, Jose Ramos, who had been dating Etan's babysitter around the time he disappeared. However, Ramos denied killing the child, but in 2004 a Manhattan judge ruled him to be responsible for the death.
Ramos is scheduled to be released from prison in Pennsylvania this year, when he finishes serving a 20-year-sentence for abusing an 8-year-old boy.