Since then, Wasser has been criss-crossing the globe analyzing the DNA of seized ivory shipments to help law enforcement officials understand where a seized stash of ivory originated and how far it’s traveled. This expensive work has been financed in part by Microsoft cofounder Paul Allen’s family foundation, as well as by grants from the US State Department, the UN Office on Drugs and Crime, and Interpol. By 2015, Wasser had analyzed 28 large shipments and identified a recurrent pattern. Over and over, tusks that showed up behind false walls or buried in fish entrails in containers as far away as Hong Kong and Malaysia could be traced back to just two regions in Africa. One was the Tridom forest, which sprawls over areas of Cameroon, The Republic of Congo, and Gabon; the other was primarily in Tanzania. He published his findings in Science in 2015.

Wasser had hoped that uncovering the world’s two major poaching hotspots would shift the ivory wars in the elephants’ favor. But it didn’t work out that way. “To our surprise, the trafficking remained very hard to stop,” says Wasser. Poachers operate in large areas they know well, and they’re often better armed than wildlife rangers. Like other forms of organized crime, poachers tend to function solely as foot soldiers; arrest 10 in the field and 10 more pop up to fill their place. To make real headway, authorities have to focus on the players further up the supply chain.

Not long after the publication of their paper in Science, Wasser’s team had a breakthrough. In October, Wasser was summoned to Singapore to sample a new seizure—4.6 tons of ivory hidden in sacks labeled as long-grain rice or sugar. He brought with him a colleague, Sean Tucker1, a forensic scientist. Together, they began the process as usual. First, they weighed all the tusks and measured the diameter of each one at its base. Then they laid them out on the floor, smallest to largest, and began arranging them further according to the length of the gum line—the distance from the tip of the tusk to where it tucks into the animal’s lip. After four days of this, Wasser usually has a pretty good idea of which tusks are part of a pair, which helps him set one aside so he’s not sampling from the same animal twice. At $110 per DNA sample, it’s as much about cost as it is about not inflating the genetic database with duplicates. But on this trip, he found hardly any pairs.

The mystery kept gnawing at Wasser and Tucker even after they returned to Seattle. Then one afternoon, Tucker burst into Wasser’s office. “Sam, did you look in the other seizures for those missing tusks?” he asked.

He hadn’t. Within days, a coder in Wasser’s lab had a new matching algorithm up and running to compare every tusk with the others in their database. It was an idea Tucker got from his days doing forensic work for the US military in Afghanistan, linking IEDs to specific terrorist cells and individuals. When the analysis finished running, “this whole picture just exploded in front of us,” says Wasser. The pairs had been there all along, they’d just been shuffled into different shipments.

DNA not only brought tusks back together, it revealed where all these seemingly unrelated ivory hauls came from. When Wasser’s team combined the genetic profiles with information gleaned from shipping documents, what emerged was a complex network connecting the largest ivory cartels in Africa. That analysis helped Kenyan law enforcement officials bolster their own evidence, including phone calls and shipping paperwork, linking the stolen caches to Feisal. He is hopeful that the intelligence he’s gathering on the Mombasa cartel will strengthen the prosecutors’ case in Feisal’s retrial. And maybe even bring down another ivory kingpin or two.

For Wasser, the convictions can’t come soon enough. On the last seizure he sampled—1,800 tusks found in Singapore earlier this year—two-thirds of them were shorter than his arm, thick as a quarter at the base. They came from animals not older than five or six. “Every year the tusks keep getting smaller,” says Wasser. Without action, the elephant DNA in his database may turn from a tool to save the species into a grim record of the animal’s extinction.

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1Correction appended, 10/01/18, 1:00 PM EDT: A previous version of this story incorrectly listed Mr. Tucker's first name as Sam.