No obvious remains found in Etan Patz excavation

Investigators remove debris from the basement of a building on the corner of Wooster Street and Prince Street in New York on Saturday, April 21, 2012 during a renewed investigation into the 1979 disappearance of 6-year-old Etan Patz.
AP Photo/Mary Altaffer

Last Updated 12:18 p.m. ET

(CBS/AP) NEW YORK - Authorities said no obvious signs of human remains have been found in a New York City basement being searched in connection with the 1979 disappearance of Etan Patz.

Investigators concluded their dig at a building in SoHo Monday where they had been searching for clues.

The FBI said Monday morning that they had finished with their work at the site. Chief police spokesman Paul Browne said the case remains a missing-person investigation, but authorities found no obvious human remains.

Patz was six years old when he vanished in 1979 on his way to a school bus.

Investigators hauled away a container filled with debris from the dig this morning, CBS Station WCBS reported. The container is being taken to a landfill on Staten Island, where it will be preserved.

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The search in SoHo began after an FBI dog indicated the scent of human remains in the room.

The basement was used at the time of the boy's disappearance as a workspace for a handyman named Othniel Miller. He has not been named a suspect.

Police and FBI agents suspended operations Sunday, in part because of the weather, but investigators did come up with a section of wall showing a "stain" that is now headed to a FBI lab in Virginia where it will be tested to determine if it is human blood.

"People who try to clean up crime scenes and leave this invisible blood behind, that's revealed by luminol spraying," explained forensics expert Dr. Lawrence Koblinksy.

Two law enforcement officials told the Associated Press on condition of anonymity that the stain was tested on site and found not to contain traces of blood.

Sources told WCBS that no skeletal, teeth or other human remains have been found.

"Fundamentally, it's about going through dirt, sifting, going carefully and looking for evidence," the FBI's Jim Margolin told WCBS. "We'll be done when we're done."