Anuchit Lumlert, a jobless 24 year old, confessed to pumping bullets into Tatiana Tsimfer, 30, and Liubov Svirkova, 25, as they sat in deckchairs drinking, Pattaya police Lieutenant General Aswin Kwanmuang said.
''He said he wanted to rob them, but had to kill them because one of the two victims saw his face,'' Aswin, who led the investigation in a city notorious as an international criminals' haven 90 miles (150 km) from Bangkok, told sources by telephone.
But investigators were not wholly convinced by the story of the man released from jail a year ago after serving a sentence for robbery.
''We didn't believe him because he didn't take their mobile phones with him as he claimed he was drunk, and we suspect he might have been hired to do the job,'' Aswin said.
The suspected killer was caught in blurry pictures on a hotel security camera arriving on a motorcycle, walking through a garden to the beach, then later returning to the same place later.
He also left the womens' wallets behind.
Police brought in experts to identify the motorcycle model, which helped track down Anuchit, who then told them where he had dumped the pistol.
Forensic tests on the pistol, found in a dumpster, matched the shell casings left at the scene, Aswin said.
There has been no official word on why a gunman would be hired to kill the two women, but there has been considerable speculation about inter-gang rivalry in Pattaya, where prostitutes from former Soviet states are common.