Koseng was charged with rebellion and illegal assembly of weapons and men for a movement pledged to separate Yala, Pattani, Narathiwat, Satun and Songkhla from Thailand.
The Appeals Court verdict reversed the Criminal Court's ruling on December 1, 2008, that dropped all charges against Koseng, but he was kept in detention pending appeal.
The lawsuit stated that from 1968 to February 10, 1998, Koseng and five Pulo members recruited members into the separatist movement and extorted protection money from businessmen in the five border provinces to buy weapons.