Deputy Mayor Ed Skyler, who is overseeing the recovery effort, said today that search officials had identified additional manholes and utility cavities that need to be examined.
The team of searchers -- including police and fire officials and forensic anthropologists from the medical examiner's office – will burrow into at least 12 subterranean areas in coming days. About five have been excavated, yielding more than 100 pieces of human remains.
Recognisable remains
The medical examiner's office said 18 were found today and the total cache of discoveries ranges from tiny fragments to recognisable bones from skulls, torsos, feet and hands. Some are as large as whole arm and leg bones.
"They will go through every grain, every piece of material carefully, and sift through it," Mr Skyler said.
The underground pockets are located along the western edge of the 6.4-hectare lower Manhattan site, underneath a north-south service road that was built in March of 2002 as the excavation was ongoing. Building the road freed up a major throughway that had been closed since the September 11 attack six months earlier.
However, when it was built, some below-ground cavities that had been used for utility and infrastructure purposes were paved over without being searched for remains. Days ago, crews doing routine work at the site opened one of those manholes and discovered human bones inside, setting off an expedition for other remains.
Relatives outraged
Families of the victims -- 40 percent of whom still have no identifiable remains -- have been outraged about the horrific discovery of the underground tombs.
They are calling for federal intervention and have demanded answers about why the search was incomplete.
Deputy Mayor Skyler said the city is focused on finding remains before it will turn to a review of any missteps.
"It's a question that should be answered, but for now our focus is on dealing with the situation and finding whatever remains are recoverable," he said.
Mr Skyler said widespread stoppage of rebuilding efforts would not be necessary, but if any portion of the rebuilding needs to pause to accommodate the search, officials will take that step by step.
Some September 11 families, however, want all rebuilding to halt until the recovery is finished.
"Their actions say remains are not a priority, they're secondary to the rebuilding," said Charles Wolf, who lost his wife and has never received any of her identified remains. "This is bringing up all the gnawing, gut-wrenching stuff inside us again."
The new cache of remains is not the first to turn up unexpectedly since the cleanup officially concluded in 2002.
Hundreds of bone fragments recently were found on the roof of a nearby skyscraper that was badly damaged in the 2001 attack and had been condemned.
Victims' relatives, who had been pushing for more careful inspection of surrounding buildings, say the recent discoveries support their argument.
Mr Skyler said that officials are reviewing the searches that were conducted at those buildings and that additional inspections may be necessary.