Authorities have concluded their search of a SoHo basement for the remains of Etan Patz, who vanished 33 years ago on his walk to the school bus stop.
No obvious signs of human remains were found, and NBC New York has learned from a law enforcement official that field tests on a concrete slab that contained a "stain of interest" over the weekend were negative for blood.
Meanwhile, dozens of items, including strands of hair, a piece of paper and other possible bits of forensic evidence, were gathered and will be analyzed further at an FBI laboratory.
"This was a worthwhile effort," NYPD chief spokesman Paul Browne said Friday, "but I don't want to go beyond that."
The Patz family was briefed Sunday on the investigation and what has been found at the site.
The search for remains of 6-year-old Patz began Thursday in the basement of a building on Prince Street. The concrete floor was torn up and investigators sifted through the dirt and soil below for evidence.
The broken-up concrete and debris will be preserved at the former Fresh Kills landfill on Staten Island, in case it is needed later, Browne said.
Some bones were found, but they were determined to be non-human, and were discovered among Chinese food takeout containers, sources said.
Sources told NBC New York that the paper found in the debris is yellow, with handwriting on it, and a piece of tape that contains two or more hairs. Its significance was not clear, but one source said it was important enough to be collected and analyzed.
At the time of Patz's disappearance, the 13-by-62 basement at 127B Prince Street was being used as a workshop by Othniel Miller, a handyman who was friendly with the Patz family.
Miller, now 75, has been interviewed by investigators several times over the years, but he recently made statements that raised their suspicions, according to law enforcement sources.
In a recent interview with investigators, he blurted out “What if the body was moved?” according to an official.
Sources also say they have evidence to suggest Patz had been in the basement before.
Miller hasn't been named a suspect, and his lawyer says he has nothing to do with the case.
Investigators have also recently questioned a second person, Jesse Snell, in connection with the re-examination of evidence. NBC New York has learned that on the morning Patz disappeared in 1979, Snell was observed at the building where police are searching now, and also worked with Miller. Investigators would not elaborate on why they met with Snell.
One other man has remained a longtime possible suspect: Jose Ramos, a drifter and onetime boyfriend of Patz's baby sitter. In the early 1980s, he was arrested on theft charges, and had photos of other young, blond boys in his backpack. But there was no hard evidence linking Ramos to the crime.
He is in prison in Pennsylvania on a separate case.
Get the latest from NBC 4 New York anytime, anywhere. Follow us on Twitter, Facebook and Google+. Get our apps here and sign up for email newsletters here. Get breaking news delivered right to your phone -- just text NYBREAKING to 639710. For more info, text HELP. To end, text STOP. Message and data rates may apply.
Published at 11:29 AM EDT on Apr 23, 2012 | Updated at 6:34 AM EDT on Apr 24, 2012