Thailand murders: Investigation 'difficult', police say
The investigation into the murders of two British tourists is proving "difficult", Thai police have said.
Hannah Witheridge and David Miller were found dead on Koh Tao on Monday.
A spokesman said officers were not certain how many weapons were used, how many attackers were involved or whether the culprits were still on the island.
Thai Police, who held a reconstruction on Thursday, said they were liaising with British police, although this has not been confirmed by UK authorities.
Investigators said they wanted to talk to three people - described as Westerners - who were seen playing a guitar near the part of Sairee Beach where the bodies were found.
A police spokesman said officers were "working around the clock" to find whoever killed Ms Witheridge, 23, from Hemsby in Norfolk, and Mr Miller, 24, from Jersey,
"We can't rule out any possibility," he said. "We have not come up with an exact number of suspects."
He said 150 officers had been deployed on Koh Tao, but added: "It's quite difficult at the minute to identify the suspects.
"Looking at the time and place this crime happened - it was really dark, late night, early morning. It's difficult to get CCTV."
Two Jersey men earlier named as "possible suspects" - brothers Christopher and James Ware - have been ruled out of the investigation and told they can leave Thailand.
A group of Burmese migrants who were detained after bloodstains were found on some of their clothes have also been eliminated from the inquiry.
Officers questioned the British brothers and 11 Burmese workers, but none of the DNA taken from suspects matched that found on Ms Witheridge or on a cigarette butt found at the scene.
BBC south-east Asia correspondent Jonathan Head said the Thai police investigation had been a "sometimes farcical performance".
He said they had initially ruled out native suspects, saying no Thai person would commit such a crime, and had also failed to seal off the crime scene or prevent people leaving Koh Tao after the killings.
The victims' bodies were found close to the beach-side bungalows where they had been staying, and a garden hoe believed to have been used in the attack was found nearby.