Thirty-three years after Etan Patz disappeared, all eyes are on the basement at 127 Prince Street in New York City as authorities use technological advances that can even detect if a body was moved to reinvestigate the cold case.
Patz, who was 6, disappeared on the morning of May 25, 1979, soon after leaving his parents' apartment at 113 Prince St., the first time he was to walk to the school bus stop by himself. The boy's 1979 disappearance sparked a massive citywide search that decades later led authorities back to handyman Othneil Miler's small basement workshop -- this time to excavate it after cadaver dogs detected the smell of human remains.
Lawrence Kobilinsky, a forensic scientist at John Jay College Criminal Justice in New York City, said vast improvements in technology since Patz disappeared, including agents that detect traces of blood and ground penetrating radar, are allowing investigators to crack "relatively old" cold cases by looking beyond what the eye can see.
"Back then there was every reason to look [in the basement] but there was no reason to break down the ground or the walls at that time." he said. "If you see something you could swab it. If anything was visible they'd be able to bring it up."
Investigators likely used ground-penetrating radar at the scene to look below the surface of concrete and drywall, he said.
"What the instrument does is it sends ultra high frequency radiation into the ground and essentially the waves, the energy travels down until it hits a discontinuity. If it hits a skeleton, they will bounce back. You can see an image on a monitor. It will go right through concrete, very, very deep into the ground," he said.
The technology is so sophisticated it is even able to detect voids in areas where a body temporarily may have been hidden, Kobilinsky said.
"If a body has been moved, that means the ground has been disturbed. A discontinuity can be picked up. It tells you this is a place worth looking at," he said.
And if the excavation finds human remains, a forensics team will be able to isolate mitochondrial DNA and match it to a maternal relative of Etan, who would share the same mitochondria.
Even traces of blood may yield clues.
"Certainly they were spraying either Luminol or BlueStar. This is a blood detection system," Kobilinsky said, adding that either agent would be able to detect traces of blood, even after 33 years.
Not only does blood remain traceable, but so does the human scent. An interview with handyman Othneil Miller two years ago after the case was reopened prompted the FBI and NYPD to put special odor-absorbing pads in his old workshop for four days.
When those pads were presented to cadaver dogs, they signaled the odor of human remains. The dogs were then brought to the basement where they again indicated the scent of human remains in an area a source said was resurfaced with concrete at or shortly after Patz disappeared.
Lynne Englebert, who trains and handles a human remains detection dog with the Institute for Canine Forensics, said cadaver dogs working cold cases is a relatively new coupling and one that was formed in the last decade.
Dogs train for their certificiation for one to two years and practice finding "old crunchy bones" with their handlers, Englebert said.
"We as human beings never lose our scent. If [a body] had been there for a while, that scent would still be there," she said, indicating that even if investigators do not find remains in the basement, it is possible human remains may have once been there before being moved.
But not everyone is prone to throw their trust to the dogs.
Kobilinsky said it wasn't clear whether the dogs are reliable.
"I'm not terribly optimistic they'll find a body. I think they will alert to things other than human remains, [such as] animal decomposition or rotting organic material," he said.
ABC News' Richard Esposito contributed to this report