Thailand murders
Investigators are to test the DNA of every male on Koh Tao Getty

Thai police are to conduct a sweeping DNA test of every male on Koh Tao in the hope of finding the murderers who killed British backpackers David Miller and Hannah Witheridge.

Authorities want to test every man who was on the island at the time of the double murder on 15 September after detectives found samples recovered from 23-year-old Witheridge that belonged to two different Asian men.

"The DNA tests reveal that the two culprits are Asians," senior police official Somyot Pumpanmuang told reporters.

"We will try to find the culprits for prosecution in a timely manner."

Twelve men, including Jersey brothers Christopher and James Ware, were released without charge last week after samples they provided resulted in negatives matches.

Police have since said the killing of Witheridge could have been motivated by "sexual jealousy" and confirmed rumours that Miller, 24, and Witheridge had become embroiled in a row with a local at a bar.

Police Colonel Kissana Phathanacharoen said: "We still believe sexual jealously is at the heart of this crime."

Miller and Witheridge, from Jersey in the Channel Islands and Great Yarmouth in Norfolk respectively, were killed about 100m from where they were staying on the island.

A post-mortem revealed Miller died of head injuries and drowning while Witheridge's death was caused by blows to her head.

The developments come as a friend of Miller feared the "Thai Mafia" was going to kill him.

Sean McAnna, who meet Miller at Leeds University and lives on Koh Tao, told the Mirror the "Thai Mafia" was trying to kill him at a 24-hour shop this morning. He has since left the holiday island.