Tests performed by the Police Hospital's Institute of Forensic Medicine also confirmed that 23-year-old Witheridge had sexual relations shortly before her death. However, institute commander Pol Maj Gen Pornchai Suteerakhun did not indicate she had been raped, according to Matichon Online.
Full DNA results may be made available as soon as late tonight.
The couple was found half-naked in a secluded area of Sai Ree beach on the Phangan district island around 6.30am on Monday.
Miller, 24, likely was killed with a blood-stained hoe found about 50 metres from the body, but today's forensics results point to an intense struggle before he died, with the victim entering the water at some point. He may have crawled or been dragged back to the beach.
Police earlier said Witheridge, who was found further from the water line than Miller, might have tried to fight an attacker trying to rape her. But as she cried for help, the killer beat her to death, said Surat Thanipolice chief Pol Maj Gen Kiattipong Khawsamang.
He told The Phuket News this afternoon, "Mr Ware is being questioned and we have taken DNA samples from him to match against those taken from the victims."He said that Mr Ware has not been arrested, adding, "We are still trying to identify an Asian man seen on CCTV coming from the direction of the murder site."
Police yesterday (September 16) began interrogating a group of Myanmar men working in the area, saying their probe was focusing on foreign workers. However, new evidence that emerged today has police again looking at fair-haired Miller's room-mate, Christopher Alan Ware, as a leading suspect.
Forensics experts in Bangkok said they found, and are now DNA-testing, blonde hairs in Witheridge's right hand. Police also found a pair of Ware's blood-stained pants from in Miller's luggage and an Apple iPhone with long blonde hairs snagged on it.
Ware, who a police official said had "left the island promptly" after being questioned and cleared by police, reportedly has been told to remain in Bangkok pending more investigation. Pol Sr Sgt Apichet Cherdguea told the German Press Agency that immigration officials have been asked to block his departure from Thailand.
"We called him in for questioning again because we found his earlier statements to be suspicious," Pol Col Prachoom Ruengthong, police chief for the nearby Koh Phangan island, told DPA.
AFP also reported a second Briton has been asked to remain in the country.
"They are not yet suspects... but we have asked them to cooperate until the case becomes clear," deputy national police chief Somyot Poompanmoung told the news agency.
In a statement issued late last night Miller's family described the engineering graduate as "hard-working, bright, conscientious, with everything to look forward to."
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