The body of an unidentified man, his face badly beaten, was found floating in the sea off Phuket on Saturday morning.
The corpse was found off Koh Nakha in tambon Pakhok, said Pol Lt Col Pathiwat Yodkwan, investigation chief at the Thalang police station, who was notified at around 11 am on Saturday.
The body was taken to Thiam beach.
Wearing a brown shirt and black underwear, the man, who was about 170cm tall, had his face beaten and teeth were broken.
Police found no identification documents on the body, which was taken to Thalang Hospital for a post-mortem examination.
The body had been discovered by the driver and staff of a tour boat taking tourists to visit Koh Khai. They then alerted police.
Investigators initially believed the dead man might have been a boat crew member who was assaulted and then thrown into the sea.
The investigation is continuing.