When 6-year-old Etan Patz disappeared from his SoHo neighborhood on May 25, 1979, America was shocked. It was the first day the New York City boy was allowed to walk to the school bus stop alone. Now, 33 years later, a break in the case has prompted the FBI and New York City police to reopen the case and try to find out what happened to Patz.

He was the first missing child to be featured on a milk carton.

Federal and local law enforcement official swooped down on Downtown Manhattan on Thursday to dig up the basement of a SoHo apartment close to Patz's home. Patz was legally declared dead in 2001.

FBI New York Office spokesman Tim Flannelly told NY 1 that the federal agents are executing a search warrant at 127 Prince Street after following leads.

A cadaver dog brought to the building's basement indicated a hit, which could indicate the current or past presence of human remains.

In 1979 the basement, now a clothing store, was the workshop of Othneil Miller, according to Good Morning America, which stated that the local handyman gave Patz $1 for helping him, the night before he disappeared. The basement was searched that year, but officials didn't dig up the floor.

Obviously there is probable cause for us to be here executing this search warrant, Flannelly said.

Investigators are also reexamining claims that the boy was abducted by Jose Ramos, a convicted pedophile and boyfriend of Patz's babysitter.

New York City apartment building where FBI agents and New York City Police were searching a basement for clues in the 1979 disappearance of Etan Patz
A New York City apartment building where FBI agents and New York City Police were searching a basement for clues in the 1979 disappearance of Etan Patz, April 19, 2012. The authorities began their search early on Thursday at the SoHo neighborhood building where the 6-year-old boy disappeared, FBI spokesman Peter Donald said. Patz, who was one of the first missing children to appear on a milk carton, was formally declared dead in 2001. His disappearance helped launch a national movement on the issue of missing children. The date May 25 was declared "National Missing Child Day" in his honor. REUTERS/Keith Bedford
FBI agents and New York City police officers stand near a New York City apartment building where they were searching a basement for clues in the 1979 disappearance of Etan Patz
FBI agents and New York City police officers stand near a New York City apartment building where they were searching a basement for clues in the 1979 disappearance of Etan Patz, April 19, 2012. The authorities began their search early on Thursday at the SoHo neighborhood building where the 6-year-old boy disappeared, FBI spokesman Peter Donald said. Patz, who was one of the first missing children to appear on a milk carton, was formally declared dead in 2001. His disappearance helped launch a national movement on the issue of missing children. The date May 25 was declared "National Missing Child Day" in his honor. REUTERS/Keith Bedford
FBI agents and New York City police officers stand near a New York City apartment building for clues in the 1979 disappearance of Etan Patz
FBI agents and New York City police officers stand near a New York City apartment building where they were searching a basement for clues in the 1979 disappearance of Etan Patz, April 19, 2012. The authorities began their search early on Thursday at the SoHo neighborhood building where the 6-year-old boy disappeared, FBI spokesman Peter Donald said. Patz, who was one of the first missing children to appear on a milk carton, was formally declared dead in 2001. His disappearance helped launch a national movement on the issue of missing children. The date May 25 was declared "National Missing Child Day" in his honor. REUTERS/Keith Bedford
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