Bone fragments found on rooftops near WTC site

NEW YORK -- More human remains from the collapse of the World Trade Center towers have been found by construction workers repairing nearby buildings almost a year after the terrorist attack.

Workers found three human bone fragments the size of small twigs on the roof of a heavily damaged 40-story building just south of ground zero, according to Port Authority Police Lt. John Ryan, who oversaw remains recovery during the nine-month excavation of the site.

Earlier this month, workers spotted a woman's pelvic bone atop a 25-story building at the southwest edge of the trade center site.

Ryan said other fragments have been found in recent weeks.

After the excavation of the 16-acre site ended in June, firefighters and police officers expanded the recovery effort to several nearby buildings. They have found bone fragments, teeth and even parts of an airplane luggage rack.

City officials had said the more thorough inspections were delayed because the work at the trade center site blocked access to the buildings, and some had to be secured before crews could enter.

The Deutsche Bank building, where the bones were found Wednesday, was the last to be searched.

"While they were searched thoroughly, some of the damage may have precluded people getting to every inch of it," Ryan said. "Now that it's being repaired or those damaged areas are being removed, they're finding things."

The discoveries this month have not prompted plans to comb the buildings again, Ryan said, but all construction crews near the trade center site have been instructed to look for human remains.

Nearly 20,000 pieces of human remains found in the debris have been logged at the medical examiner's office. Of the 2,829 people killed, 1,379 have been identified.

About half of the remains did not yield enough DNA for standard tests, but officials said Thursday they will begin using a new procedure next month that they expect will lead to more identifications.

The city worked with Orchid GeneScreen of Dallas to adapt a test that examines pieces of DNA shorter than 100 base pairs.

Billions of chemical base pairs make up human DNA and form its signature double helix. Forensic experts generally work with DNA samples of about 400 base pairs, but as DNA degrades, it shrinks, decreasing the number of base pairs.

The DNA in trade center remains was further damaged by heat and humidity, according to Dr. Robert Shaler, chief of forensic biology at the medical examiner's office.

The new procedure looks at single nucleotide polymorphisms, or snips, tiny variations in the smallest building blocks of DNA. Each person is estimated to have between 3 million and 10 million snips.

Scientists already use the procedure for disease research, but the medical examiner's adaptation is new.