DEVELOPING: The search of a basement for missing 6-year-old Etan Patz ended Monday, the FBI told FoxNews.com, with no obvious human remains found in the decades-old cold case.

"The FBI has concluded the on-site portion of the search," FBI spokesman Peter Donald said. "The street and local businesses will be re-opened."

Authorities began ripping up the basement's concrete floor with jackhammers and saws last Thursday in their renewed search for Patz, who disappeared on May 25, 1979, while walking alone to his school bus stop for the first time. A cadaver-sniffing dog had recently indicated the scent of human remains in the basement located in Manhattan's SoHo neighborhood.

The basement, just steps away from the boy's home, is the former workspace of retired handyman Othniel Miller, 75, who was seen with Patz the night before he disappeared.

The exhaustive search of the space, however, yielded no obvious human remains or conclusive evidence in the case, authorities said Monday.

A source close to the case said over the weekend that authorities are testing a stain found on one of the basement's walls. The source said when investigators sprayed Luminol on the wall, they detected "an organic substance" -- "possibly blood." The stain has been sent to the FBI lab in Quantico, Va., for further testing.

The source also confirmed reports that an unrelated molestation claim prompted police to reexamine Miller, who is now being described as a main "person of interest" in the Patz case. Miller's ex-wife told law enforcement last year that she divorced her husband in 1986 after learning he had sexually assaulted her 10-year-old niece a few years after Etan disappeared, the source said.

Miller's workshop was on the route the boy would have taken to his bus stop, authorities said.

The boy's disappearance in 1979 prompted an extensive search by police and nationwide media attention. Etan's photo was one of the first of a missing child to appear on a milk carton.

Investigators have long focused their attention on Jose Ramos, a drifter and onetime boyfriend of Etan'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.

Ramos, now 68, reportedly admitted trying to molest Etan on the day of his disappearance, but denied abducting him or killing him. Ramos has never been charged criminally in the Patz case and is currently serving a 20-year prison term in Pennsylvania for abusing an 8-year-old boy there. Ramos is scheduled to be released from prison in November.

In 2002, Etan's father, Stan Patz, had Etan declared dead in order to sue Ramos in civil court. A civil judge in 2004 found Ramos to be responsible for the disappearance and presumed death of the boy, after he disobeyed the judge's orders to answer deposition questions under oath for a lawyer representing Etan's parents.

Prosecutors, however, lacked enough evidence to charge Ramos criminally.

In 2010, Manhattan District Attorney Cyrus R. Vance Jr. decided to reopen the case.

The focus of the investigation shifted to Miller after investigators received new leads in the case. Miller, originally from Jamaica, was interviewed after the boy disappeared and had what authorities deemed a solid alibi at the time.

Authorities, however, noticed that Miller had a newly cemented concrete floor around the time of Etan's disappearance, but opted not to dig it up.

A source close to the case said "there is truth to that" when asked about news reports that Miller blurted out, "What if the body was moved?" when taken by police to the basement in recent days.

Miller has so far not been named a suspect and has denied any wrongdoing through his lawyer.

The Patz family, who has remained in the same apartment for 33 years in the hopes their son would one day return home, has declined to comment on the recent developments.

"To the hardworking and patient media people, the answer to all your questions at this time is no comment," reads a note outside their apartment, just one block away from dozens of FBI trucks and police cars. "Please stop ringing our bell and calling our phone for interviews."

"Stan Patz, 3E."

The Associated Press contributed to this report.