NEW YORK — Ralph Geidel cannot remember a time when he wasn't obsessed with finding things that had been lost or discarded — forgotten marbles on the playground, old coins, false teeth and silver jewelry at the beach. And he was good at it.

This is why, on a warm, spring day, Geidel crouched on his knees on the roof of a lower Manhattan skyscraper, his face inches from a pile of gravel, looking for something precious.

Looking for traces of his brother, and others killed at the World Trade Center.

Gary Geidel was one of 11 members of an elite fire squad who died on Sept. 11, 2001. Not a granule of his remains has been identified, and nearly five years later, Ralph Geidel found himself on this roof, still searching.

He stopped suddenly, plucked a small, eggshell-colored object between his fingers and slipped his reading glasses onto his nose for a better look.

"Could be part of a vertebrae," he thought.

The piece would join a growing collection. Some 760 specks and slivers of human bones have been discovered in recent months, after demolition began on this 41-story former bank tower known as the Deutsche Bank building, just south of where the World Trade Center once stood.

Gary Geidel is not the only one who is still missing. Of the 2,749 people who were killed that day, the remains of some 1,150 have not been found.

Their families have nothing — not a sliver of a bone — left of their loved ones. And they have long since given up any hope of finding recognizable human parts.

Searchers recovered whole bodies at first — 291 victims were found intact. But as they dug into the 10-story mound of debris with rakes and machines, it was mostly just fragments.

Ralph Geidel, a retired firefighter, was among the thousands of searchers at ground zero from the start. Wearing his old FDNY coat, a photograph of his brother fastened to his firefighter helmet, Geidel checked for patterns and signals that might offer clues to hidden remains.

"You look for something that doesn't belong among that rock, the concrete, the steel, the papers and all the other stuff," he said. "You just kinda develop an eye for that, something that doesn't quite mix with everything else — certain shapes, like hands.

"I found a lot of hands."

Eventually, more than 20,000 parts were collected as the debris was excavated, sifted and carted away. Many were recovered at a second site, the former garbage dump in Staten Island where debris was hauled and combed again.