A Thai court on Thursday sentenced two Myanmar migrants to death for the murder of two British backpackers on a resort island last year, in a case that raised questions about police competence and the treatment of migrant workers in Thailand.

Human Rights Watch called the verdict "profoundly disturbing," citing the defendants' accusations of police torture that were never investigated and questionable DNA evidence linking them to the crime.

Win Zaw Htun and Zaw Lin, both 22, have denied killing David Miller, 24, and raping then murdering Hannah Witheridge, 23, last year on the island of Koh Tao. Their defense attorney said they planned to appeal.

Miller and Witheridge's battered bodies were found Sept. 15, 2014, on the rocky shores of Koh Tao, an island in the Gulf of Thailand known for its white sand beaches and scuba diving. Autopsies showed that the young backpackers, who met on the island while staying at the same hotel, suffered severe head wounds and that Witheridge had been raped.

The killings tarnished the image of Thailand's tourism industry, which was already struggling to recover after the army staged a coup just months earlier in May 2014 and then imposed martial law.