Another 300 or so human bone fragments have been found in recent days on the roof of a skyscraper badly damaged by the collapse of the World Trade Center, officials said Thursday.

Workers have been removing toxic chemicals and trade center dust from the former Deutsche Bank building before they begin dismantling it floor by floor. They found 10 bone fragments on the roof when the cleanup began last fall and another 80 in recent weeks.

Two fire department battalion chiefs and retired firefighters joined in the search for remains this week after some relatives of people killed in the attacks of Sept. 11, 2001, complained that recovery experts should help the construction workers.

The bone fragments, most less than 1/16 of an inch long, were found during the past four days in gravel on the roof of the 41-story skyscraper, said Ellen Borakove, spokeswoman for the city medical examiner's office.

Recovered remains are taken to a DNA lab for testing, and those that are identified are turned over to families. Those that can't be identified will be stored at a World Trade Center memorial.

Part of the trade center's 110-story south tower tore through 15 stories of the Deutsche Bank building when it collapsed. The bank building, covered in black netting, has remained vacant, contaminated with asbestos, trade center dust and other chemicals.

The Lower Manhattan Development Corp., which bought the building for $90 million and is paying to tear it down, has added an archaeologist and an investigator from the medical examiner's office to oversee the work.

The development group hopes to complete the search for remains and clean the building of toxins by June.