Thai beach murders: DNA investigation into death of British backpackers Hannah Witheridge and David Miller 'incompetent at best'

The two Burmese men convicted of the crime are urged to file a complaint with an international regulator

Hannah Witheridge and David Miller, who were murdered on a beach in Thailand in September 2014 (PA)

Police in Thailand may have to face an international regulator over the way they handled the investigation into the murder of British backpackers Hannah Witheridge and David Miller.

International legal and DNA forensics experts have advised Zaw Lin and Wai Phyo - the two Burmese immigrants sentenced to death over the killings - to make a formal complaint and demand a retrial.

The bodies of Ms Witheridge, 23, and Mr Miller, 24, were found on the island of Koh Tao in September 2014 with severe head injuries.

Ms Witheridge had been raped and Mr Miller had been drowned in the sea after being struck on the head.

But experts have now said the DNA investigation by the Thai Police Forensics Laboratory was at best incompetent - and in the worst case scenario framed the two men.

One of the team told the London Evening Standard: “I have spoken to the Australian Asia Pacific Laboratory Accreditation Cooperation which is willing to intervene.

“My feeling is the two young Burmese rather than being executed would be suing the authorities in a western country — and their lawyers should do that in Thailand.”

The police investigation has come under intense scrutiny after allegations came to light that the two men were tortured until they admitted their guilt.

Myanmar migrant workers Zaw Lin, center, and Wai Phyo, rear, arrive at a provincial court in Surat Thani province, Thailand (AP)

They later recanted and pleaded not guilty.

In January, Ms Witheridge’s sister Laura attacked the conduct of the Thai authorities in a post on Facebook.

She said “the vast majority of Thai police” were corrupt, making the country a “dangerous trap” for tourists.

She hinted that she thought Thai nationals were responsible for the killings and that she received death threats throughout the trial - with one person suggesting the murderers had only “half completed the job”.

Ms Witheridge claimed they told her parents to “go home and make another one” if they were upset at losing their daughter.

She said: “What if I told you that, since we lost Hannah, there have been many more suspicious deaths on Koh Tao. You probably haven’t heard of them, as not all were British nationals. The deaths, where possible, are covered up as suicides and accidents.

“This would have happened with Hannah, if it had not been for the hideous brutality of her passing.”

Ms Witheridge’s family has not formally condemned or praised the conviction of the two men.

Thai police have repeatedly denied any wrongdoing.