A Thai court sentenced two Myanmar migrant workers to death on Thursday after convicting them of the 2014 murders of two young British tourists on a holiday island in a case mired in controversy and a dispute over DNA testing.

The battered bodies of backpackers Hannah Witheridge and David Miller were found on a beach on the island of Koh Tao in September 2014. Police said Witheridge, 23, had been raped and bludgeoned to death. Miller, 24, also suffered blows to his head.

After weeks of pressure to solve the case, police arrested Myanmar migrant workers Zaw Lin and Win Zaw Tun and later said the two had confessed to the crimes.

The brutality of the murders dented Thailand's image as a happy-go-lucky holiday paradise and raised serious questions about its treatment of migrant workers.

The verdict and sentence follow an investigation and trial that triggered allegations of police incompetence, mishandling of evidence and DNA tests and torture of the suspects. Both later retracted their confessions saying they had been made under duress.

The verdicts came after 21 days of witness hearings in a trial that began in July and ended in October.

As is customary in Thailand, where trials have no jury, a judge delivered the verdict and sentence and said the DNA tests by investigators were carried out to acceptable standards and the DNA found on Witheridge matched that of the defendants.

The debate over DNA samples that police say linked the two suspects to Witheridge were at the heart of the trial. Defense lawyers had asked to retest DNA samples but authorities issued conflicting statements on DNA evidence and, at one point, said that it had been used up.

No independent retesting of DNA evidence has been done.

"We believe what happened today represents justice for Hannah and David," said Michael Miller. "The Royal Thai Police conducted a thorough and methodical investigation ... evidence against the two was overwhelming."