Sources also tell us that the FBI and the NYPD met Sunday with the parents of Etan, to update them on the investigation.
The search will resume Monday after investigators temporarily shut down the operation on Sunday.
The FBI wouldn't go into specific details as to why it abruptly decided to call it quits for the day, only saying it was for "operational reasons".
"It's in part because of the weather, we can't go into details but we've concluded the operations for the day," said FBI spokesman Jim Margolin.
Day four of this investigation included the collection of yet more evidence from the basement of 127 Prince Street.
Roughly 35 members of the Evidence Response Team started the day around 8 Sunday morning.
Agents have finished ripping up the basement's concrete floor and are now digging deeper, 4 to 6 feet down.
They're hoping to find Etan Patz's remains or any clues, in this heart wrenching mystery.
"If they could solve it, bring it to a close, that would be amazing, to find out what happened, if it was here," said SoHo resident Steve Rodriguez.
6 years old at the time, Etan vanished on May 25, 1979 while walking to the school bus stop.
The day before he spent time in the very same basement, helping Othneil Miller, a handyman who used the space as a workshop.
The 75 year old was cleared at the time but is now considered a person of interest, although he maintains he is innocent.
Officials won't say what, if anything, was found in the basement.
However sources tell Eyewitness News that a stain found on a concrete wall is being tested.
As for how long all of this will continue, the FBI says, they'll be done, when they're done.
"It's about going carefully through dirt and sifting it carefully and looking for evidence," said Margolin.
For decades, the prominent case of a missing 6-year-old had a prime suspect: an admitted child molester in a Pennsylvania prison. Although the inmate was never criminally charged in Etan Patz' 1979 disappearance, he was found responsible in a wrongful-death lawsuit.
Authorities said they had yet to find any new evidence as of Friday, and the police commissioner and the FBI said they wouldn't discuss any possible suspects. It's unclear what the renewed probe may turn up, if anything.
But if it leads definitively away from Pennsylvania prisoner Jose A. Ramos and to someone else, it could create a legal conundrum: one person held accountable for the boy's death in civil court while another became the focus of a criminal case.
On Friday, investigators were using jackhammers and saws to carefully break through the basement's concrete floor, pulling rubble out and carrying it out of the building with gloved hands, as an anthropologist stood by in case any human remains were found; the work concluded for the day around 6 p.m. but was expected to continue over several days. The debris was to be taken elsewhere and tested, a process that could last into next week, chief police spokesman Paul Browne said.
Police were using a chemical that can spotlight traces of blood and expected that X-ray equipment could help them peer behind walls, though some walls were being removed, Commissioner Raymond Kelly said.
"We're hopeful that we can bring some level of comfort to the parents, perhaps find some - obviously, the body of this poor child - but evidence that may lead to a successful investigation in this case," Kelly said. He was a lieutenant working on organized crime cases when Etan (pronounced AY'-tahn) vanished on the first day he was allowed to walk to his school bus stop alone.
As for whether authorities were optimistic, he said, "I really can't say."
Investigators decided to refocus their attention on the building after recently speaking again to Miller, whom they had interviewed several times over the years, according to a law enforcement official who spoke to The Associated Press on condition of anonymity because the investigation is ongoing.
Among the first vanished children to appear on a milk carton, Etan became a symbol of a movement to draw attention to child safety - the day of his disappearance, May 25, became National Missing Children's Day. The case has bedeviled investigators as leads emerged and fizzled over the years; Etan, never found, was officially declared dead in 2001.
Ramos, a drifter whose girlfriend was Etan's sometime baby sitter, has been publicly floated as a possible culprit since the 1980s. Now 68, he is serving a 10-to-20-year sentence in Dallas, Pa., after pleading guilty to abusing an 8-year-old boy at a campground there. He is due to be released in November. Efforts to reach lawyers who have represented him were unsuccessful Friday.
A former federal prosecutor who had worked on the case, Stuart GraBois, declared in 1998 that he believed Ramos was behind Etan's disappearance and death; efforts to reach GraBois on Friday were unsuccessful. A Manhattan civil court judge held Ramos responsible in 2004, saying that his refusal to answer some questions amounted to not responding to the suit. The judge ordered him to pay $2 million to Patz' father, Stan.
Police investigated leads to Ramos at various points, including a 2000 search of the basement of the building where he lived in 1979. But the Manhattan district attorney's office concluded there wasn't enough evidence to charge him, or anyone else. Former DA Robert Morgenthau, who led the office from 1975 to 2009, declined to comment Friday.
Current DA Cyrus R. Vance Jr. spent time with Stanley Patz while running for office in 2009 and pledged to reopen the case if elected.
After the investigation resumed in 2010, authorities considered if they should take a fresh look elsewhere since decades of eying Ramos had never yielded anything conclusive, according to another person familiar with the investigation, who also spoke on condition of anonymity to discuss its workings.
The basement Miller had used "started to seem more and more like at least a viable place to start," the person said.
Should the new direction lead to a new suspect, that wouldn't automatically negate the civil court's finding against Ramos.
But he might be able to get a court to reconsider it, legal experts said.
"This would be such a colossal change from what was thought to be the case at the time, I think the courts would probably, to be just, find some kind" of avenue to reopen the case, said Annemarie McAvoy, a former federal prosecutor who now teaches at the Fordham University School of Law.
Associated Press writers Jim Fitzgerald, Samantha Gross and Karen Matthews, photographer Bebeto Matthews and researcher Barbara Sambriski contributed to this report from New York, and writer Matt Moore contributed from Philadelphia.
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