NEW YORK (CBSNewYork/AP) — More possible pieces of human remains have been found during the sifting of newly uncovered debris from the site of the September 2001 terrorist attacks, the New York City medical examiner’s office said.

Twenty-one potential human remains were recovered Wednesday, bringing the total found during the current effort to 39, the office said.

DNA testing is required before any remains can be identified.

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.

Investigators will spend 10 weeks trying to find remains in that debris, city officials said.

The last time the city did a comprehensive sifting of debris was in 2010.

Since 2006, the remains of 34 previously unrecovered victims were identified through DNA.

Of the 2,752 victims killed at the World Trade Center site — previously known as ground zero — 1,634 have been identified.

(TM and © Copyright 2013 CBS Radio Inc. and its relevant subsidiaries. CBS RADIO and EYE Logo TM and Copyright 2013 CBS Broadcasting Inc. Used under license. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed. The Associated Press contributed to this report.)

Watch & Listen LIVE