Etan Patz: Basement searched in boy’s 1979 disappearance (VIDEO)

Dozens of New York City police officers and FBI agents began digging up the basement of a building Thursday said to be connected to the case of Etan Patz, a 6-year-old boy who vanished 33 years ago.

Etan disappeared after leaving his parents' Manhattan apartment to catch the school bus on May 25, 1979. It was the first time his parents had let him go off to school alone, according to The Associated Press.

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The building on Prince Street is connected to a handyman who had contact with Etan just before he disappeared. Authorities recently got an alert from a cadaver dog brought into the building's 13-by-62-foot basement, a law enforcmement official told NBC New York.

"We're looking for human remains, clothing or other personal effects," New York Police Department spokesman Paul Browne told CNN. "It's a very painstaking process."

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Authorities planned to remove the room's drywall and test the bricks for blood evidence using advanced forensic techniques that were not available three decades ago, ABC News reported.

The floor will also be dug up in a search for human remains, clothing or other evidence, according to ABC.

Etan's disappearance was a media sensation in 1979. The boy's face was among the first to appear on milk cartons, and President Ronald Reagan declared May 25 to be National Missing Children's Day, according to the AP.

No one has ever been charged in the case, but the boy's father, Stanley Patz, sued an incarcerated drifter and admitted child-molester, Jose Ramos, who had been dating Etan's babysitter around the time he disappeared, the AP reported.

A judge declared Etan legally dead in 2001. According to The New York Times, District Attorney Cyrus R. Vance Jr. agreed to reopen the case in 2010.