Deputy Mayor Cas Holloway said in a memo Friday that DNA testing will continue until every possible identification can be made. The sifting is expected to continue for about 10 weeks on Staten Island.
City officials say about 60 truckloads of construction debris have been collected around the site over the past 2½ years. A skyscraper will replace the twin towers.
Some 2,750 people died at the World Trade Center in the 2001 attacks. So far, 1,634 people have been identified.
The chief medical examiner's office is leading the operation. It has identified 34 victims and 2,345 possible human remains of previously identified victims since 2006.
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