Dr Esmond Bradley-Martin, one of the world's leading ivory trade investigators, was found dead in his house in Nairobi, Kenya, the Star newspaper reports.
It says the 75-year-old American former UN special envoy for rhino conservation, had a stab wound in the neck.
His wife reported his death after returning to the house from a walk early in the evening, reports say.
A police investigation is now under way.
Dr Bradley-Martin published a number of investigative reports on rhino and ivory smuggling in Kenya and the trade in China, Laos and Vietnam.
