KOH SAMUI • A Thai policeman described the harrowing moments when he discovered the bodies of two British holidaymakers on Koh Tao island, as the high-profile trial of two Myanmar migrants charged over their deaths opened.

Zaw Lin and Win Zaw Tun have both pleaded not guilty to the murder in September last year of Mr David Miller, 24, and the rape and murder of Ms Hannah Witheridge, 23, in a case that has tarnished Thailand's reputation as a tourist haven.

The two men, who have been in custody on neighbouring Koh Samui since October, arrived at the court in a prison van with their feet shackled. They face several charges - including murder, rape and robbery - and if found guilty could face the death penalty.

Family members of the two British backpackers were also present as the trial began yesterday and the prosecution questioned the first witness, a policeman who found the bruised and battered bodies.

The officer described the awful scene as he discovered the lifeless Mr Miller "face down" on the shallow surf and the body of Ms Witheridge farther up the beach. Police have said she was raped as well as beaten. Their murders, just a few hundred metres from the main tourist drag in Koh Tao, sent shockwaves across the sleepy idyll in the Gulf of Thailand immensely popular with backpackers and divers.

But the prosecution has been marred by allegations of a bungled investigation with the defence team claiming the migrants, who worked for low wages in the tourism trade, were used as scapegoats by an under-pressure police force.

One of the team's key demands has been the opportunity to independently test controversial forensic evidence against its clients.

After the opening of the trial, the judge said a decision on this would be made today, according to an activist for a migrants group helping to fund the defence case, as journalists were asked to leave the small courtroom to make room for family members. Both families have appealed for privacy for the duration of the trial, which is expected to take place over 18 staggered days between now and September with a verdict due in October.

The killings came as the country's vital tourism industry was beginning to recover from months of violent street protests that culminated in the May 2014 military coup.

The case also shone a light on Thailand's many underpaid and often exploited Myanmar migrant workers who fill the lucrative tourist sector. The pair's defence team has long criticised the police investigation, claiming the crime scene was contaminated and that its clients were tortured into admitting guilt.

Both men retracted their initial confessions, saying they were coerced into making them. The defence had also complained about not being given access to the forensic evidence, despite the court initially ruling that the defence could run its own independent tests.

The forensic material from the crime scene has been used by Thai police and prosecutors to insist they have charged the right men.

The victims' families have also previously said they have confidence in the case after British investigators reported back to them following a visit to Thailand late last year. AGENCE FRANCE-PRESSE