Scores of people rallied at ground zero Saturday to remember the fallen, and call for a more thorough search for the bone fragments still being found at the World Trade Center site.

Activists have said they aren't convinced that enough is being done to recover any small bits of remains that might still be hidden among other debris at the vacant Deutsche Bank building, which was damaged beyond repair in the trade center collapse.

Richard A. Gould, a professor of anthropology at Brown University, said he is concerned the teams scouring the building are using tools too crude to find every bone fragment.

"What the site needs is a careful, systematic clearing job," he said. "So far, that hasn't happened yet."

The search for remains at the skyscraper resumed this month after a two-month break ordered by environmental officials.

More than 600 human bone fragments have been found on the 41-story tower. A majority were on the roof.

Workers are also removing asbestos and other toxic materials from the building as a prelude to demolishing it.

The recovery of remains is being overseen by the city's medical examiner, and that office's forensic anthropologist, Dr. Bradley Adams, an expert who formerly worked with a military task force recovering the remains of soldiers from Korea and Vietnam.

Ellen Borakove, a spokeswoman for the medical examiner, said the city's methods are careful and thorough. She invited families with concerns to appoint their own specialist to observe the operation.