Forensic Identification of 9/11 Victims Ends

The letter to families will say that as forensic technology advances, more of the DNA samples may ultimately be identified.

For now, the unidentified remains -- nearly 10,000 samples -- will be placed in the soon-to-be-built memorial at Ground Zero. They will still be accessible, however, if scientists choose to examine them further.

But for families of nearly half of the victims, the memorial must now remain a final resting place.

ABC News' Bill Blakemore filed this report for "World News Tonight."