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Why the Towers Fell
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Ground Zero DNA

(running time 01:33)

September 5, 2003

NARRATOR: Almost half of the people lost at the World Trade Center, roughly 1,200 victims, have not yet been identified. Techniques for analyzing DNA, the genetic blueprint unique to each person, have helped with the task of identification.

ROBERT SHALER (NYC Medical Examiner's Office): We have over 1,521 identifications so far. If we did not ever have DNA typing, we would have had about 736 identifications and we would have stopped working in May of 2002.

NARRATOR: As shown on PBS's NOVA, the fires from the attacks burned for months. In initial tests, researchers found that fire and water damage rendered the DNA unusable in about 61 percent of the remains recovered from the wreckage.

ROBERT SHALER (NYC Medical Examiner's Office): They were spraying water on it to keep it cool so the workers could get in there and find the people, and the warm, moist environment is very bad for DNA, it's very bad for tissues.

NARRATOR: Standard DNA typing techniques require longer strands of DNA than were recovered from the victims' remains. But Shaler and his team are now reanalyzing some of the samples with new forensics techniques, including a variation on a paternity test, created specifically for much smaller fragments of degraded DNA. Even with these advances, identifications have slowed considerably from this time last year. But Shaler remains hopeful.

ROBERT SHALER (NYC Medical Examiner's Office): People like to have hope, and so this is something they can hang their hat on and say there's hope for the future. I don't know how realistic that hope is, but I still think there's hope.

NARRATOR: I'm Brad Kloza.

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