NAIROBI, Kenya — Esmond Bradley Martin, a Kenya-based American conservationist whose dogged investigations of the elephant ivory and rhino horn trades over decades were seen as critical in efforts to protect the threatened species, was found stabbed to death in his Nairobi home, Kenyan authorities said Monday.

International conservationists were shaken by news of the violent death of Bradley Martin, a distinctive figure known for his shock of white hair and a handkerchief tucked into his jacket breast pocket whose off-beat appearance belied the passion and rigor that he channeled into his work in far-flung parts of the world. He sometimes worked undercover, and at considerable personal risk, while still managing to extract valuable information from traders and dealers.

Esmond Martin Bradley, an expert on the illegal ivory trade was found stabbed to death in his home in the Nairobi, Kenya, police say. Brian Inganga / AP file

"He was an inspiration" and a pioneer of research on the illegal wildlife trade, said Julian Rademeyer, author of "Killing for Profit," a book about rhino horn trafficking. "He was prepared to go to some of the most remote places on earth to dig up information."

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A family member found Bradley Martin's body with a stab wound to the neck on a bed in his house on Sunday, said Nicolas Kamwende, head of criminal investigations in the capital, Nairobi.

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The motive for the killing of Bradley Martin, who was in his mid-70s, was unclear. There was no immediate suggestion from authorities of a link to his work, which often delved into the illegal activities of traders and traffickers whose exploitation of African ivory and rhino horn for international buyers, many of them in Asia, has fueled the mass slaughter of the iconic species.

The area in Langata, the Nairobi suburb where Bradley Martin lived, has some security barriers and guards on main roads. However, some properties are large with big gardens that could be accessible to an intruder.

An Associated Press reporter who visited Bradley Martin at his home in 2015 noted that the conservationist didn't appear to be slowing down despite his advancing years. Bradley Martin talked animatedly for about an hour, leafing through research papers and reeling off statistics about rhino poaching. He was both precise and excited, seemingly eager to make every minute of discussion count.

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Bradley Martin, often working with co-investigator Lucy Vigne, conducted many surveys for the Save the Elephants conservation group that "shone a powerful spotlight on the wildlife markets around the world that are sucking ivory, rhino horn and countless other African species into their maw," the group said. The work provided "a solid foundation for action to close them down," it said.

The pair's most recent report, published in 2017, concluded that Laos has the fastest growing ivory trade in the world. Bradley Martin was working on research on Myanmar when he was killed.

Bradley Martin releases the "Wild Ivory Report" which identified the U.S. as "one of the world's leading ivory markets" in this May 5, 2008, file photo. Tim Sloan / AFP - Getty Images file

"Esmond and Lucy have produced report after report that documented in detail the exploding demand for illegal ivory in China, Vietnam and Laos that fed into the worldwide move to ban domestic ivory trade," Allan Thornton, president of the Environmental Investigation Agency, a non-profit group based in Washington.

The pair also reported on drops in the price of ivory in China, "providing the world community with key information that underlined the importance of China's domestic ban in reducing ivory demand in the world's biggest market," Thornton said in an email to The Associated Press. China banned its ivory trade at the beginning of this year.