The case is especially frustrating to those outside Laos, who say Mr. Vixay appears untouchable as long as he remains in his home country, where, they say, officials have refused to do a thorough investigation despite the reams of evidence presented to them. And without stopping him, wildlife officials and investigators say, they have little hope of breaking down a business empire that they say connects the African savanna to the Asian jungles and ultimately to customers of ivory and traditional medicines in Vietnam and China.

“He is the single largest known illegal wildlife trafficker in Asia,” said Steven Galster, the executive director of Freeland, a counter-trafficking organization that has been trailing Mr. Vixay for eight years. “He runs an aggressive business, sourcing lucrative wild animals and body parts wherever they are easily obtained. Every country with commercially valuable wildlife should beware.”

Freeland has been instrumental in building a case against Mr. Vixay, and was the source of the vast majority of the documents reviewed for this article, including business contracts and Laotian customs documents that attest to the scale of his operations. Founded in Bangkok more than a decade ago, Freeland is staffed by current and former law enforcement officials from Britain, the United States, Thailand and a number of other Asian countries, and is financed partly by the American government.

The nonprofit organization, which works closely with government officials in Africa, Asia and the United States, also provided entree for The New York Times to some of those officials. The Times interviewed authorities from Thailand, China, South Africa, Laos and Vietnam.

The booming trade in exotic wildlife has been fueled by rising wealth in China and Vietnam and the demand there for things like the scales of the pangolin, which are consumed in the unproven belief that they help lactating mothers.

Mr. Vixay, who is in his 50s, has met this growing demand for animals like snakes, lizards and turtles from his base in the impoverished countryside of Laos, a thinly populated country bordering Vietnam and China and known for its widespread corruption.