Current forensics will allow authorities to look into hollows and to perform sophisticated DNA analysis on any potential evidence.
"It's a joint FBI-NYPD search for human remains clothing or personal effects," Browne told reporters outside the building after investigators entered using a search warrant.
Patz vanished on May 25, 1979 in the SoHo neighborhood of Manhattan while walking alone to a school bus stop for the first time.
For the Patz family, it has been more than three decades of agonizing investigations and years of wondering what happened to their blond son with the gorgeous smile.
In an interview with "20/20" in 2009, the boy's father Stan Patz said, "I still gag with fear that this child must have felt ... when he realized he was being betrayed by an adult."
The case had been dormant until Vance Jr. reopened the case. Former DA Robert Morgenthau had declined to proceed with the case, citing insufficient evidence.