When notorious ivory trader Edouodji Emile N’Bouke was brought to court in 2014, he plead not guilty. This seemed unlikely, as authorities had just seized 1,540-pounds of ivory from his shop and home in Togo. But N’Bouke claimed the ivory was all old stuff, acquired well before 1990 when the international ivory ban took effect. Was he lying?

Normally, authorities would have no way of knowing. But in this case, samples from N’Bouke’s stash had undergone a cutting-edge forensics analysis, revealing that some of the ivory came from elephants killed just four years earlier. N’Bouke was found guilty and sentenced to 15 months in jail.

Now, the same powerful tool has been applied not just to a single case, but to hundreds of samples of ivory from around the world. The analysis has revealed that most of the ivory entering into the illegal trade today comes from elephants killed less than three years ago, researchers report in Proceedings of the National Academy of Sciences. This finding suggests that the recent surge in elephant deaths—savannah-dwelling populations have declined by 30 percent in the last seven years, while elephants living in forests dropped 62 percent from 2002 to 2013—are intimately linked with the illegal global trade in ivory.

“There’s been controversy for some time as to how to determine the killing rate of elephants,” says lead author Thure Cerling, a distinguished professor of geology, geophysics and biology at the University of Utah. “This shows that everything that has been seized comes from animals that died very, very recently.”

Ivory’s age has been the subject of an ongoing debate among conservationists. Some have suspected that older material is leaking out of government storage facilities, or that traders hoard tusks for many years before sneaking them onto the black market. If true, this would mean that the poaching crisis isn’t as acute as it might seem, since much of the ivory entering into the market today comes from elephants long dead. Others insist that the ivory currently flooding markets in Asia must be from recently killed animals, given the rate at which elephants across Africa are being slaughtered.

To settle this debate, Cerling and his colleagues used carbon-14 dating, a well-established method that relies on radiocarbon produced by nuclear tests carried out in the 1950s and 1960s. In that time period, the U.S. and Soviet Union detonated so many bombs that they changed the concentration of carbon-14 in the atmosphere by a factor of two. The isotope has been slowly changing since then, and scientists refer to compiled measurements of its concentration over time as the bomb curve.

Additionally, every living thing on the planet contains carbon-14, acquired either through the atmosphere (if you’re a plant) or by eating plant-based food (if you’re an animal). Measuring the amount of carbon-14 in a biological sample and then matching it to corresponding values in the bomb curve tells scientists when the tissue formed, plus or minus six months. This method has been used in forensics to date mummified corpses found in the desert, for example, or to determine how long it takes for cocaine to travel from forest to urban consumer.

Until now, however, no one had applied the method to the ivory trade—mostly because of its expense and the fact that only about a dozen labs around the world are able to perform these tests. Cerling and his colleagues analyzed 231 ivory specimens collected from 14 large seizures made between 2002 and 2014 in Africa and Asia. The researchers found that 90 percent of the samples came from elephants that died less than three years before their ivory was confiscated. The oldest piece was from an elephant killed 19 years before its ivory was seized; the youngest, just a few months.

The dates also shed light on global patterns of the ivory trade: researchers found that ivory from East Africa tends to enter into the trade faster than ivory from the Tridom region of Cameroon, Gabon and Congo, where forest elephants live. That difference might reflect dwindling elephant populations in the Tridom, Cerling says, making it more difficult to collect enough ivory to form a worthwhile shipment. Alternatively, it could be that East Africa has more established illegal networks for moving contraband goods, or that savannah elephants are simply easier to find and kill.

The paper provides a convincing link between recent poaching and illegal trade of ivory. It also presents a practical way to keep ivory thieves more accountable in the future, says Edouard Bard, chair of climate change and ocean sciences at the College de France in Paris, who was not involved in the research. “One can no longer hide and pretend ignorance, in the hope that illegal objects such as ivory will remain untested,” he says.

For instance, while China, Japan and the European Union still have legal domestic trade of antique ivory, much of what is legally for sale today could be from recently poached animals that traders have laundered into the market, says Cerling. “With this method, you can tell exactly when the animal died and see if the ivory is actually as old as the person who is selling it claims it to be,” he says. However, N’Bouke’s groundbreaking case notwithstanding, this method is less likely to be applied in Africa, where many seizures are being made but funds and technical expertise are lacking.

While (relatively) new technology can help researchers understand how the trade works, it certainly won’t end the practice on its own, points out Elizabeth Bennett, vice president of species conservation at the Wildlife Conservation Society, who was not involved in the research. Instead, Bennett says, countries should focus on shutting down ivory trade within their borders. “If all domestic markets globally were illegal, it would be much more difficult to sell the newly poached ivory,” she says. “And without a ready market, the incentives to poach and traffic are reduced or removed.”