KOH SAMUI, Thailand — Ten months after two British tourists were killed on a resort island in Thailand, prosecutors called their first witnesses Wednesday in a case marked by claims that the accused — two migrant workers from Myanmar — were tortured into confessing.

Following widespread attention, the case has been called a test for Thailand’s justice system and its treatment of migrant labourers.

The battered bodies of David Miller, 24, and Hannah Witheridge, 23, were found last Sept. 15 on the rocky shores of Koh Tao, a scenic island in the Gulf of Thailand known for its scuba diving. Autopsies showed that the young backpackers, who had met on the island while staying at the same hotel, had both suffered severe head wounds and that Witheridge had been raped.

The first policeman on the scene, Lt. Jakrapan Kaewkao, told the court that he received a call at 6:30 a.m. that morning about two tourists’ bodies found on the beach. He said he arrived to find a gruesome sight.

“I found a man’s body lying on the beach with seawater lapping his body,” said Jakrapan, the prosecution’s first witness. “Then I found the woman’s body behind the rocks.” The rocks were spotted with blood, he said. The two bodies were several meters (yards) apart and both were mostly unclothed, with Witheridge’s body bearing signs of physical assault, he said.

Miller’s father and brother and Witheridge’s mother and brother were in the courtroom, and there were about a dozen people from Myanmar, including a representative from its embassy in Bangkok.

In the small courtroom on Koh Samui, an island near Koh Tao, the accused sat in orange prison uniforms with their legs shackled.

The two men, Win Zaw Htun and Zaw Lin, both 22, were arrested in early October and initially confessed to the killings but then retracted their statements, saying they were extracted through beatings and threats, which police deny. Human rights groups repeatedly called for an independent investigation and raised concerns that the men might be scapegoats.

The accused were indicted on several charges related to the murders and to illegally working in Thailand. Prosecutors say they have a solid case against them that includes DNA evidence linking them to the crime.

Journalists were initially allowed into the courtroom, which seats about 30 people, but then ushered out to make room for relatives of the victims, diplomats and others attending the trial.

A second witness, Dr. Chasit Yoohad, gave testimony about his examination of the victims’ bodies. He said he also performed a medical checkup of the two accused, and found them in good health. He said he asked through a translator if they had committed the crime, and they replied that they had.

“We hope the truth will be revealed,” defence lawyer Nakhon Chompuchat said as he headed into the courtroom. “We hope the mechanism of justice in Thailand … will have the same standards of international countries.”

Twelve days have been scheduled for prosecution witnesses, but it is unclear when the proceedings will be concluded.

From the start, the case raised questions about police competence. Investigators faced a variety of criticisms, including their failure to secure the crime scene and their releasing of several names and pictures of suspects who turned out to be innocent.

Under intense pressure to solve the case, which drew global attention, police carried out DNA tests on more than 200 people on Koh Tao.

Concerns that the men were tortured by police originated with advocates for migrant workers, who are often abused and mistreated without the safeguard of rights held by Thai citizens. The British government also expressed concern to Thai authorities about the way the investigation was being conducted. As a result, British police were allowed to observe the case assembled by their Thai counterparts.

The victims’ families travelled to Koh Samui for the trial and issued a joint statement.

Witheridge’s family urged the media not to focus on the “speculation, rumour and theory” that has surrounded the case, making “an unthinkable time harder to bear.”

Miller’s family said that just hours before he died, their son had called home and described the beauty of Koh Tao and the friendliness of the Thai people. “Over the coming weeks we hope to gain a better understanding as to how such a wonderful young man lost his life in such idyllic surroundings in such a horrible way,” they said.

About 2.5 million people from Myanmar work in Thailand, most as domestic servants or in low-skilled manual jobs such as construction, fisheries or the garment sector.

The gruesome killings tarnished the image of Thailand’s tourism industry, which has been struggling to recover after the army imposed martial law and staged a coup in May 2014.