Two men suspected of killing endangered tigers in Thailand have been arrested, a U.S. conservation group said Thursday, and the key evidence turned out to be cell phone images of them with their prizes.

A phone with the images was seized after a gun battle between Thai park rangers and suspected poachers in a protected area, the Wildlife Conservation Society said in a statement.

Poachers have killed a mountain gorilla at Bwindi Impenetrable Forest National Park.

The area conservation manager, Mr Pontius Ezuma, said the 12-year-old black-back gorilla died last week of injuries it sustained after it was speared on the chest by unknown poachers at Biyumba in Kanyonza Sub-county, Kanungu District.