The bodies of David Miller, 24, and Hannah Witheridge, 23, arrived in Bangkok late yesterday for forensic examination.
They were found naked and beaten to death early Monday near a beachside bungalow on the island, a diving hot-spot near Koh Phangan in the Gulf of Thailand.
A bloodied hoe was discovered 35 metres from the murder scene.
Three male Burmese migrant workers were held for questioning but ruled out of the probe later yesterday, southern regional police commander Panya Maman told AFP.
“They were very far from the scene … it was probably not them,” he said, adding that DNA samples had been collected from the men.
He did not give details of any further leads as the manhunt on the small, normally tranquil island stretched into a second day without an arrest.
Police have also cleared a number of British tourists who travelled with the victims of any involvement in the killings.
Earlier yesterday, local television showed Thai authorities searching several shacks belonging to Burmese migrants on Koh Tao.
The family of David Miller said he had been in Thailand on a “well-deserved break” in between finishing a degree in civil and structural engineering at Leeds University in June and starting a master’s.
Miller, a “talented” artist who had been due to leave Thailand yesterday, was “hard-working, bright, conscientious, with everything to look forward to,” his family said in a statement issued by the British Foreign Office.
“We all adored him,” the statement read. “He will be sorely, sorely missed.”