Police will request help from the United States' Federation Bureau of Investigation to test semen found in the body of a female British backpacker brutally murdered on the resort island of Koh Tao this week.
DNA testing technology in Thailand could only identify whether human secretions came from a male or female, said deputy police chief General Somyot Pumpunmuang, while the FBI had "sophisticated technology".
"We will ask the FBI to help identify the DNA in the semen we found - whether it belonged to an Asian or European," he said yesterday.
The bodies of Hannah Witheridge and fellow British national David Miller, both 24, were found on Monday morning on Koh Tao, in Surat Thani province. Autopsies revealed they were brutally beaten, while Miller was drowned during the deadly attack.
Somyot, who will become police chief next month, said he would travel to Koh Tao today to inspect the crime scene and follow up on the latest developments of the investigation.
"This is a big case and the premier has been very concerned about the matter," he said.
Meanwhile, residents on Koh Tao are offering a reward for information that leads to the arrest of the killers, Koh Tao mayor Chaiyan Turasakul told Agence France-Presse.
"At this point we are offering Bt50,000 (S$1,966) for anyone who can provide clues which leads to the arrest of a suspect. The money comes from donations from the people of Koh Tao," Chaiyan said.
Prime Minister General Prayuth Chan-ocha said in his weekly televised address to the nation yesterday that he had ordered police to bring the culprits to immediate justice.
"Progress has been made continuously although it is not known yet who are the killers," he said.
"The authorities concerned have been assigned to ensure safety at tourist attractions. People and volunteers must also engage in assisting and monitoring for the sake of safety."
Somyot revealed that the latest inspection of the crime scene unearthed a cigarette butt at a spot on the island where traces of Witheridge's DNA was found. He said it was likely that she met her attackers at the spot and had a conversation there.
Pol General Jaramporn Suramanee, an adviser to the Royal Thai Police Office who visited Koh Tao on Thursday, said on that day that several pieces of evidence had been found at the scene.
He visited the scene after DNA samples collected from the body of Witheridge did not match those of the 12 suspects.
Jaramporn was speaking after searching an area near the crime scene towards the sea during low tide on Thursday night.
He simulated what might have happened including focusing on the distance between the location where the bodies were found and a hoe believed to be the murder weapon.
Witnesses near the crime scene told police they saw three men near in the area on the night of the murders.
A tourism police commander, Maj-General Atichai Ti-amart, said police were also looking for a foreign woman captured on CCTV running near the crime scene.
Police investigators continued to gather more evidence yesterday, focusing on trying to identify an Asian man seen in CCTV footage at the time of the murder.