Almost half of WTC victims identified

The desire for the identifications among victims' family members is strong.

NEW YORK (CNN) -- New York's medical examiner predicted Saturday his office will ultimately identify 2,000 of the 2,823 people who died in the Sept. 11 attacks on the World Trade Center.

So far, the medical examiner's office has identified 1,229 victims, or 44 percent of the total number of people listed as dead. Initially, authorities predicted they would not be able to identify more than half of those killed.

"I'll be very disappointed if we don't identify 2,000 people by the end of the year," said Dr. Charles Hirsch, the city's medical examiner.

That number would represent 71 percent of the total fatalities. But Hirsch acknowledged that the figure is an estimate.

"It's what our gut tells us, based on emerging technology and what samples we have to work with," he said.

However, since the decay of tissue accelerates with time and high temperatures, authorities are unlikely to be able to identify all of the victims, Hirsch said.

"Some people just don't exist anymore, due to the high heat and passage of time," he said.

Authorities collected 19,700 tissue samples from World Trade Center rubble at the Fresh Kills landfill on Staten Island during the World Trade Center cleanup. The samples were taken to the medical examiner's office.

Landfill closes Monday

No more samples are expected to arrive. A ceremony Monday morning will mark the closing of the landfill.

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The effort has resulted in more than simple identifications. "I think we learned a lot -- some things to do and some things not to do," Hirsch said. "We hope our experience will make it easier for other examiners for future disasters.'

The biggest lesson: the value of planning. "We put in place the thinking and a lot of the infrastructure before it occurred," he said. Though he and his staff are now working normal business hours, that was not the case last fall. "At first there was no clock and no calendar."

They have not had to shoulder the load alone. A federal response team of volunteers -- including medical examiners -- pitched in from around the country immediately afterward and stayed on until the end of June.

Five hundred of the identifications have been made using solely DNA technology. Most of the other identifications have been made using standard technology, including dental X-rays, fingerprints and personal belongings.

The identification process has required more than scientific expertise, he said. Throughout the painstaking effort, he and members of his staff have worked closely with family groups, seeking their suggestions and probing them for details of the victims' bodies that might help in making identifications, such as scars, tattoos, implants.

Any further identifications will all be made using DNA technology, he said.

During the procedure, DNA from tissues culled from the rubble is compared with DNA taken from hair and toothbrushes brought in by family members of the victims.

Families support quest for identification

The desire for the identifications among victims' family members is strong. Only about two dozen families chose not to respond to requests for such material, he said.

Hirsch's team has also employed two new methods of identification.

One uses mitochondrial DNA, which is inherited from the mother only. Any maternally related person may provide a sample for comparison with a biological sample.

In the first use of the technology in a large-scale disaster, thousands of biological samples have been sent to Celera Genomics Group, a private laboratory with offices in Bethesda, Maryland, and San Francisco, California, Hirsch said.

Another new technique is called SNIP. Short for single nucleotide polymorphism, SNIP does not require the long strands of DNA required by standard analytic procedures. Instead, even tiny bits of tissue degraded by time and heat may still yield the identities of their owners, he said.

Though the procedure remains experimental, Hirsch said he hopes the technology will enter the realm of accepted practice within a few months. "If we can validate this, it will be the first time used for forensic analysis."

With nearly 20,000 tissue samples in storage and advances in technology continuing to expand the limits of what is possible, Hirsch predicted his job may never be completed.