David Miller and Hannah Witheridge
David Miller and Hannah Witheridge were killed on Koh Tao on 15 SeptemberFacebook

Thai police have turned to local night owls to help them find the killers of British tourists David Miller and Hannah Witheridge.

Detectives in Koh Tao are appealing for information from people who usually stay awake from midnight to 6am and those who wake early and go walking between 2am and 4am.

Lieutenant general Panya Mamen said 179 people had had their DNA sampled after Miller and Witheridge were battered to death with a hoe and wooden stick on 15 September, reports the Bangkok Post.

Mounting evidence also gave Mamen hope the murderers would soon be found.

"We are starting to be confident. Anyone who was in the radius of 600 metres from 2am to 4am, woke up, went out for a walk and carried some other connection are in the group that we will examine," he said.

Reports also claim police want to question footballers who had been taking part in a tournament and partied at the AC Bar on the island the day before the 24 and 23-year-olds were killed.

The protracted investigation has been criticised by observers for its sclerotic pace, much to the anger of Thailand's Prime Minister, Prayuth Chan-ocha.

"If I rush them [the police] too much, the wrong suspects will be arrested. We're trying to base the probe on scientific evidence as much as we can, and no one will be made a scapegoat. If their DNA does not match, they are not suspects," he told a British reporter.