Esmond Bradley Martin was willing to risk it all for rhinos and elephants, working dangerous undercover operations that put him face-to-face with nefarious criminals, all for the chance to unearth clues about the demand for illicit ivory and rhino horn, which is fueling a growing poaching crisis in Africa.

Oftentimes, it worked. Martin’s daring helped him penetrate black markets the world over, in countries like China, Japan, Nepal, Laos and Vietnam. Armed with important details about how and where ivory and rhino horn changed hands and where the illicit substances eventually ended up, Martin published his findings in reports he shared with conservationists and non-profits. Formerly the United Nations special envoy for rhino conservation, his research is widely credited with bringing an end to China’s ivory trade.

“His meticulous work into ivory and rhino horn markets was conducted in some of the world’s most remote and dangerous places and against intensely busy schedules that would have exhausted a man half his age,” said Iain Douglas-Hamilton, founder of Save the Elephants.

Unfortunately, Martin has written his last report. The anti-poaching world was rocked on Sunday, when the 75-year-old conservationist was discovered by his wife, stabbed to death at their home in Nairobi Kenya.

“It’s a tragedy and a setback,” Philip Muruthi, vice president of species protection for the African Wildlife Foundation, told National Geographic. “He brought the data. He brought the information to really inform people on the demand side of the trade and what the markets are all about.”

Police are calling the attack a botched robbery, and to date, no information beyond the initial report has surfaced that would indicate this to be true one way or the other. However, a Guardian article on the subject notes that “there are also concerns that the murder may have been related to Bradley Martin’s work,” but does not attribute those concerns to any sources, anonymous or otherwise.

Martin had recently returned from Myanmar and was still working on his report when he was killed, according to the BBC.

Whether or not his death is linked directly to his work does not change the fact that conservation and environmentalism are dangerous businesses, with nearly four activists killed every day in 2017.

The risk is especially high for those who dedicate their lives to thwarting poachers. A staggering 82% of wildlife rangers, who are notoriously under-equipped, say they’ve faced life-threatening situations. More than 150 rangers have been killed in the past decade in Virunga National Park alone, making the park in the Democratic Republic of Congo the world’s most dangerous.

And now rangers and activists on the front lines have lost an irreplaceable ally who was fighting the same fight with many of the same risks, albeit on the opposite end of the supply chain. Regardless of the details and circumstances surrounding Martin’s death, rhinos, elephants and conservationists will miss his work.

“He leaves a gap that must be filled quickly,” Murithi said.

Is there another Esmond Bradley Martin undercover somewhere, risking everything to bring to light the nitty-gritty details of the ivory and rhino horn markets in an against-all-odds effort to save Africa’s cherished wildlife?

We can only hope so, and that he or she is safe and making rapid progress in the war against poaching. For elephants and rhinos, time is running out.