The office says 21 potential human remains were recovered Wednesday. That brings the total found during the current effort to 39.
About 60 truckloads of debris that could contain tiny human bone fragments have been unearthed by construction crews working on the new World Trade Center tower in recent years. City officials say investigators will spend 10 weeks trying to find remains in that debris. The city's last such effort ended in 2010.
Some 2,750 people died at the World Trade Center in the Sept. 11 attacks, but remains of only 1,634 people have been identified.