Eighth Region Police Command commissioner Pol Lt-Gen Panya Mamen identified the first suspect as Mon.
He is the brother of a village headman in Koh Tao.
He was arrested after evidence which police collected were examined and proved he was involved, he said.
He also said another suspect is also a son of that village headman. But he has already to Bangkok.
He said both suspects were captured by CCTV cameras and the police have gathered enough evidence to implicate them in the murders.
He said the southern police were coordinating with the metropolitan police to hunt him down, and expected to apprehend him today.
The southern police chief also assured the public that there was no arrest of scapegoats in this murder case as it now is a focal attention of the world.
He also dismissed any suggestion of local mafias or influential people that could twist the investigation with promise that local influence would pose no obstacle to the police investigation.
Instead the police will eliminate all these mafias, he said.
Meanwhile a police source said the police are also looking into the cooperation of those who helped to arrange the suspect to escape. They also will be arrested.