Police in Thailand have admitted the investigation into the brutal murders of two British tourists is proving "quite difficult" as they revealed they do not know how many people were involved in the killings.
Five days after the bodies of Hannah Witheridge, 23, and David Miller, 24, were found with severe head wounds on a beach on the island of Koh Tao, a spokesman for Royal Thai Police insisted officers are "working around the clock to find the culprits" amid fears the investigation has stalled.
Post-mortem examinations revealed Miss Witheridge, from Great Yarmouth, Norfolk, died from head wounds while Mr Miller, from Jersey, died from severe blows to the head and drowning. A bloodstained garden hoe, believed to be the murder weapon, was found nearby.
Police Colonel Kissana admitted it was "difficult to say" if the killers were still on Koh Tao and police were unable to confirm if there was more than one murder weapon.
He said: "We're working closely with local police, local people and local authorities. The deputy commissioner is in the area for two days in a row.
"We can't rule out any possibility. We have not come up with an exact number of suspects.
"Last night we conducted a crime scene reconstruction to get a sense of what happened."
He said 150 officers had been deployed on the island and senior police officials had met Miss Witheridge's "deeply distressed" family.
"It's quite difficult at the minute to identify the suspects," he said.
"Looking at the time and place this crime happened - it was really dark, late night, early morning. It's difficult to get CCTV.
"We are committed to finding the culprits."
He added that Thai police had been liaising with their British counterparts.
Meanwhile, two British brothers who were questioned by police have been told they are free to return home, police have confirmed.
Christopher and James Ware, childhood friends of Mr Miller who had been speaking with officers but were never detained or declared to be suspects, were told they can fly back to Jersey.
Police say they are still looking for three Westerners who were seen playing a guitar near the scene on Koh Tao's main Sairee beach.
A group of Burmese migrants who were interviewed by police after bloodstains were found on their clothes have also been eliminated from inquiries. No matches were found between them and DNA found on Miss Witheridge and a cigarette butt at the scene.
The family of Miss Witheridge arrived in Thailand yesterday and had an emotional meeting with Thailand's deputy police chief, in which they were given updates on the investigation into her death.
The bodies of the two young Britons have been moved from a forensic hospital in Bangkok and arrangements are being made by the Thai foreign ministry for them to be repatriated, according to reports.
Thailand's military ruler has apologised for suggesting that foreign visitors to his country's world-famous beaches might be unsafe wearing bikinis.
In the face of mounting criticism, General Prayuth Chan-ocha said: "I apologise that I have spoken too harshly ... I didn't mean to criticise or look down on anyone. Today I can guarantee that Thailand is still safe ... I wanted to warn (the tourists) to be careful."
Earlier this week he claimed that foreigners visiting the south-east Asian country think "they can do whatever they want, wear bikinis wherever they like ... (but) will they be safe?".
He was quoted as saying: "Can they be safe in bikinis ... unless they are not beautiful?"