Esmond Bradley Martin, one of the world’s top ivory investigators, who also helped persuade China to shut down its legal rhino horn and ivory trades, has been killed in Nairobi.

The 75-year-old American was found dead in his house in the Kenyan capital with a stab wound to his neck on Sunday (Feb. 4). Kenyan police said they have yet to identify his attackers, but suspect it was the result of a botched robbery, according to agencies.

As a leading conservationist, Martin was known for infiltrating and documenting illegal sales of ivory and rhino horns and then publishing the details of his findings.

His work exposing the scale of ivory markets took him across the world from the United States to Congo, Nigeria, Angola, China, Hong Kong, Vietnam, Laos, and Myanmar.

His research on the dynamics of illegal wildlife markets also provided governments with the data they needed to clamp down on, and eventually shut down both legal and illegal exchanges.

Martin’s death comes shortly after China enforced a ban on sales of ivory. The country was the world’s largest importer of ivory, and the trade was responsible for the deaths of as many as 30,000 elephants in Africa a year.

Ivory smuggling had also done a lot of damage to China’s alliances with African nations, given the high demand for elephant tusks and rhino horns for use in traditional medicine and decoration.

Agencies