All species of rhinoceros are protected under U.S. and international law, and all black rhinoceros species are endangered.

WSJ: 3 charged in smuggling horns of endangered rhinos

At the Metropolitan Police stores, Sergeant Knox shows me a horn from a black rhinoceros, brutally hacked away from the animal's head.

BBC: UK laws 'spurring trade in endangered species'

Native to Africa, the black rhinoceros is classified as a critically endangered species, according to the Convention on International Trade in Endangered Species of Wild Fauna and Flora.

BBC: Three charged in rhino horn smuggling ring