Still, scientists are trying to identify more victims. Bode Technology Group, the Virginia company contracted to work on 9/11 remains, has developed new and encouraging processes to extract identifications from bone samples which previously came up blank.

Families and some elected officials are calling for the intervention of the Joint POW/MIA Accounting Command, a military forensic unit known for finding missing soldiers from long-ago wars.

But Bradley Adams, the city's chief forensic anthropologist used to work for the military unit, and he insisted that this was "the most meticulous recovery project that I've ever worked on — the size of the fragments that are being recovered is really impressive, and I have complete confidence. You couldn't do a better job."

Ralph Geidel is renowned among the searchers. In his retirement, the 48-year-old lives in Northern California, where he looks for gold in old mines and waterways. His lifelong passion for treasure hunting even landed him in South Dakota, looking for dinosaur bones.

At ground zero, he had an uncanny knack for finding remains.

"He picked things out — it was amazing — that nobody else could see," said Bill Butler, a retired firefighter who spent months in the rubble, searching for his son, Tom. "We'd go through stuff and you'd glance over it, thinking it was part of construction material or furniture or items from the building, but Ralph seemed to have a special eye for body parts and remains."

Geidel's father and younger brother, both firefighters, were also there, and the family suppressed their grief to look for Gary, the oldest of four siblings. Obsessed and tormented, Geidel imagined he heard the dead screaming.

"I'd follow the scream until I found somebody and then the screaming got less and less," he said. "The more people I found, the better I felt."

But he never found Gary.

"Who knows what's where, what's been lost?" he says. "There's a million reasons he could still be missing, and a million places he could be."