Defence lawyers in the trial of two Burmese men accused of killing two British backpackers on a Thai resort island last year said on Wednesday they would focus on the reliability of crucial DNA evidence.

British tourists Hannah Witheridge, 23, and David Miller, 24, were killed last September. Their bodies were found on a beach on Koh Tao, a Thai island in the Gulf of Thailand popular with backpackers and SCUBA divers.

The killings drew outrage in Britain and raised questions about the competence of Thai police and the treatment of migrant labourers in Thailand.

Following weeks of pressure on authorities to solve the crime, Thai police said in October that Burmese workers Zaw Lin and Win Zaw Htun, both 22, had initially confessed to the killings. Both later retracted their statements, saying they had been tortured into confessing.

The murder trial, which began earlier this month, has been consumed by allegations of police incompetence and evidence mishandling by defence lawyers. Rights groups have also claimed the men are being used as scapegoats because of their status as foreign migrant workers in Thailand.

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At the heart of the trial is a debate over DNA samples that police say link the two suspects to Witheridge’s body.

Police have issued conflicting statements about the DNA, including that some was lost or “used up”. They later took back that statement, saying DNA samples had not been lost.

Defence lawyers said that evidence would remain the focus when the trial resumed on Wednesday.

“Questioning today will focus on the DNA of the accused and the collection of the DNA,” lead defence lawyer Nakhon Chompuchat told Reuters.

A court on the island of Koh Samui, where the trial is taking place, ordered this month that remaining forensic evidence in the case be sent for reexamination at the Thai justice ministry’s central forensic institute.

“We still have not seen any progress on the request to see the DNA gathered by police,” Nakhon said.

READ: Background on Koh Tao murders