A second Burmese man has admitted to killing British tourists Hannah Witheridge and David Miller in Koh Tao.
Thai police arrested three men in connection with murder of the British backpackers, who were beaten to death with a garden hoe last month.
Major General Kiattipong Khawsamang said two of three migrant workers being questioned had admitted murdering the pair.
The third man has denied involvement but police still believe three people were involved in the attacks.
A huge investigation was launched after cleaners found the bodies of Witheridge, 23, and Miller, 24, on a beach on 15 September.
Both victims suffered severe head injuries at the hands of their killers and a post-mortem revealed Witheridge was raped by two Asian men before she died.
Every male who was on the island at the time of the deaths was swabbed for DNA in the hope of catching the culprits.