The New York city medical examiner's office says it has exhausted all efforts to identify the remains of those killed at the World Trade Center.
In the three-and-a-half years since the attack, forensic scientists have identified the remains of nearly 1,600 of the dead. But the families are now being told that the limits of DNA technology have been reached, leaving more than 1,100 of the victims unidentified.
For many of the families, any hope that their loved ones' remains might be found had slipped away long ago.
Forensic teams worked around the clock after the attacks to identify the dead via DNA from toothbrushes and combs supplied by the victims' families. During the work, the remains were kept in refrigerated trucks outside the coroner's office.
Nearly 20,000 pieces of bodies were found in the ruins — more than 6,000 small enough to fit in five-inch test tubes. The most matched to one person exceeded 200. More than 800 victims were identified by DNA alone.
Nearly 10,000 unidentified parts have been freeze-dried and vacuum-sealed for preservation in case advances in forensic technology some day enable scientists to identify the remains.
In many cases, the fierce fires, the crushing debris and other factors prevented scientists from extracting usable DNA.