Two years ago Wasser and his colleagues at the University of Washington published a continent-wide map of genetic fingerprints for African elephants in the Proceedings of the National Academy of Sciences.
To make this map, Wasser's team had sequenced DNA recovered from nearly 500 samples of dung collected from elephants in 23 African countries.
Ample roughage in the elephants' diets helps slough off plenty of cells from the intestines, making DNA easy to extract from dung.
Wasser's team found that they were able to identify which countryeven which game preservenew dung samples came from.
Bill Clark, secretary for the Interpol Working Group on Wildlife Crime, asked Wasser to match DNA from the seized ivory to his genetic map.
But getting DNA out of the tusks proved to be a challenge.
Drilling or grinding ivory heats it, destroying any DNA present, so Wasser's research group borrowed a technique from forensic dentistry.
The team sealed slices of ivory sawed from tusks in a tube along with a stainless steel plug, then froze the tube to -240°F (-150°C).
Using a rapidly reversing electromagnet to shake the metal plug, they smashed the ivory into a fine powder from which DNA could be extracted.
When Wasser's team compared 75 samples from the illegal shipment to their genetic map, they found that all of the ivory came from Zambia.
"This blew Interpol's mind," Wasser said.
Just months before the shipment was seized, Zambia had requested permission for a one-time sale of stockpiled ivory. That request was subsequently denied.
"Wasser's work is potentially extremely useful," Interpol secretary Clark said.
"Regrettably it is still quite new and being applied for the first time, so we have not yet any experience with prosecutions or the technique's admissibility as evidence in court."
But just knowing where the ivory is coming from could help, Clark said, by identifying poaching hot spots where efforts to prevent hunting could be focused.
Meanwhile the illegal trade continues. On May 10 customs officials in Hong Kong announced they had confiscated a shipment of 600 African elephant tusks.
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