"Two of the suspects raped and killed Ms Witheridge while another one witnessed the murder," Pol Lt Gen Panya Mamen, commissioner of Provincial Police Region 8, said on Sunday (September 28) after a meeting with investigators to discuss case updates.
The murders of Hannah Witheridge, 23, and David Miller, 24, occurred in the early hours of the morning after they left AC Bar.
"We're confident we have a very high chance of finding the suspects," the senior police officer said.
"I'm not worried [about high public expectations] because I know how much the probe has been progressing. We just have to follow forensic results," he added.
Investigators yesterday seized three guitars from a shelter of Myanmar workers for examination. One of them was hidden without anyone admitting ownership but the other two had owners, police sources said.
Police also have also approached seven Thai football players living in Koh Phangan, Koh Samui and Muang districts for DNA samples. They joined a traditional football match on Koh Tao on September 14.
Pol Lt Gen Panya said police have set up a special team to probe rumours, unconfirmed information and tips from the public.
Meanwhile, results from more than 200 DNA tests conducted in Koh Tao should be ready today (September 29), the head of the police forensic unit says.
Pol Lt Gen Kamrob Panyakaew, chief of the Office of Police Forensic Science, said his staff were working 24 hours a day analysing DNA samples.
Two different semen samples collected from Ms Witheridge's body are the basis for the DNA analysis. Testing confirmed the semen belonged to Asians.
Tourism and Sports Minister Kobkarn Wattanavrangkul visited Koh Tao yesterday in a bid to restore confidence.
Ms Kobkarn proposed a tourism centre should be set up on the island to improve security measures.
She said tourist police officers would work full-time at the centre and the ministry would bring in two helicopters for use in the event that air transport was necessary.
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