Shortly after the 9/11 terrorist attacks, authorities said they would continue searching until they could return to every family something of their lost relative.
But now, families of nearly half of the 2,749 who died in the attacks will soon receive letters from the New York City Medical Examiner's Office saying it has reached the limits of forensic science for now. At most, they say, only two or three more bodies are likely to be identified.
"I'm confident they did everything they could to do what they had to do with the DNA," said Monica Iken, who lost her husband, Michael Iken, who worked on the 84th floor of Tower Two. "It's still that empty feeling that you have -- that unless you live it it's kind of hard to explain."
Remains of 57 percent of the victims were identified using DNA, dental records or bits of jewelry. Families who received notification that their loved one's remains had been identified say it makes a difference.
"Instead of believing in the twilight zone -- is he dead, is he alive? is he dead, is he alive? -- we could move on," said Talat Dalani, whose 26-year-old son died in the towers. "There's a place he is buried. A sense of closure."
Over the past six months, working with the most damaged DNA samples, examiners have managed to identify only eight more people.
"The problem with the trade center is that when the pieces are that small, [they] can get mixed in with other debris from the actual building, and it creates an incredibly difficult task to separate things out," said Dr. George Bauries, a former FBI evidence response expert.
Many knew this day would come. After the attacks, experts predicted that the violence of the collapse and the intense heat of the fires meant that at most 25 percent of the victims would be identified.
The multiplicity of remains for each victim is also a reason why the medical examiner's office is fairly certain there is only hope for a few more identifications.
The fact that more than 50 percent of the victims have already been identified is remarkable, they say.
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."