Two decapitated bodies were found in the sea near Koh Sak, Pattaya, on Thursday.
Pattaya police said they were alerted after locals found two unidentified bodies of a man and a woman near an abandoned yacht at 4pm.
The male body was found 500m off Koh Sak, the Bangkok Post reported.
He is believed to have been dead for between 10 and 15 days, said Police Lieutenant Supan Sophee, an investigator at Pattaya police station.
He was wearing red underwear and a blue shirt with embroidered Thai words, which were translated as "60th anniversary of Namsin Insurance".
There were also two tattoos on his left thigh, one of a chicken and another of a tiger.
The woman's body was retrieved about one nautical mile from the male body. She was wearing a brown long-sleeved T-shirt and had an eagle tattoo on her left leg.
The police have yet to determine the age and nationalities of the two victims.
The bodies were taken to a Bangkok hospital for an autopsy.
The Pattaya city sea rescue unit had spotted a large white yacht 800m from where the woman's body was found.
The yacht, a catamaran known as a Lagoon 440 model and whose name was not provided by the police, appeared to have been ransacked. Its door was locked from the outside.
Witnesses told the police that they saw the boat dock in the area about 10 days earlier.
Yesterday, the police contacted the Marine Department to help identify the yacht's owner.
Koh Sak, a small island shaped like a horseshoe, is 10km west of Pattaya, and 600m from Koh Larn.
This article was first published on August 30, 2014.
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