Thai police have matched DNA found on the body of British tourist Hannah Witheridge to that of two Asian men.
The bodily fluids of two men found during forensic investigation are now thought to belong to Asian men, police revealed.
But officers say they do not know if the killer is still on the island of Koh Tao, where the body of Witheridge, 23, was found on Sairee beach alongside that of David Miller, 24.
Witheridge, who is from Great Yarmouth, suffered severe head wounds and Miller died from blows to the head and drowning, post-mortem examinations show.
A garden hoe, thought to be the murder weapon, was found with Witheridge's blood on it nearby. Investigators are searching for a separate blunt metal object used to kill Miller.
There is now doubt over whether Miller was with Witheridge on the night of their deaths, as Thai police had previously claimed, according to a Mail Online report.
British backpacker David Miller may have been coming to the aid of Hannah Witheridge as she was being attacked on a Thai beach when the pair were brutally murdered, new evidence suggests.
Traces of the 23-year-old woman's DNA and that of one other person were found on a cigarette butt around 50 yards from where her body was found.
There are suggestions that Witheridge shared the cigarette with her attackers before she was killed.
'Confusing' case taking longer to solve than expected, say Thai police
Police in Thailand had previously admitted the investigation into the murders is proving "quite difficult" as they did not know how many people were involved in the killings.
The bodies of Witheridge and Miller, who met on the island of Koh Tao while travelling, were discovered six days ago.
Thai police insisted officers were "working around the clock to find the culprits" amid fears the investigation was stalled after two false leads in the last week.
Around 150 officers have been deployed on the island to track the killer or killers, said senior police on Friday. Police officials have also met Witheridge's "deeply distressed family" in recent days and liaising with British counterparts, who are assisting the investigation.
Police Colonel Kissana said of the difficulties in finding the culprits: "Looking at the time and place this crime happened – it was really dark, late night, early morning. It's difficult to get CCTV."
Two British brothers, Christopher and James Ware, were questioned by police over the murders. The pair, who are childhood friends of Miller, were told they could fly back to their home in Jersey, and were never detained or declared to be suspects.
A group of Burmese migrants who were interviewed by police after bloodstains were found on their clothes has also been eliminated from inquiries. No matches were found between them and DNA found on Witheridge and a cigarette butt at the scene.
Thailand's military ruler came under fire this week for suggesting that foreign visitors to the country's beaches could be unsafe if wearing bikinis. He was quoted as saying: "Can they be safe in bikinis… unless they are not beautiful?"
The bodies of Witheridge and Miller 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.