Investigators were battling thick fog in the Colombian mountains Thursday to reach the site of a plane crash that killed all 15 people on board, including a politician. Locals and farmers were the first to arrive at the crash site, the transport ministry said, which lies in a rugged, densely covered tract of the Andes' eastern range with highly changeable weather. Advertisement AdvertisementAdvertisement AdvertisementSwaths of the surrounding countryside are controlled by Colombia's largest guerrilla group, the National Liberation Army, better known by its Spanish acronym ELN. While the cause of the crash was not immediately known, the Colombian aviation authority highlighted poor weather conditions. "We recorded persistently adverse weather conditions at the impact site," Colonel Alvaro Bello, head of accident investigation at Colombia's Civil Aeronautics Authority told a press conference.