Two suspects charged with murdering British tourists Hannah Witheridge and David Miller in Thailand have reportedly retracted their confession, saying they were tortured by police.
There is growing international concern over the murder investigation after a Thai forensic expert said the police's supposed evidence "contradicted the principles of forensic science", while Amnesty International has demanded an investigation into possible human rights abuses.
Thai prosecutors have rejected a police report into the killings, claiming it lacked "crucial information".
Thai police claim two Burmese workers confessed to the murder and rape of Hannah Witheridge, 23, and to killing David Miller, 24 on the backpacker island of Koh Tao on 15 September. They were charged last week.
The two men have already been paraded by police at a news conference and took part in a re-enactment of the brutal crime on the beach where the Britons' bodies were found. They wore protective vests and helmets to prevent them being attacked by the watching crowds.
But the suspects have now told a lawyer from the Myanmar embassy that they didn’t kill Witheridge and Miller, according to reports.
They said police beat them until they confessed, and one man also alleged police threatened him with electrocution if he did not confess to the crimes.
The lawyer, Attorney Aung Myo Than, said he met with the suspects and saw they were covered in bruises, according to The Bangkok Post. He said they were “pleading with the Myanmar (Burmese) government to look into the case and find out the truth”.
According to Amnesty International, other reports suggest police have beaten the various Burmese migrant workers who they have questioned in connection with the murders, and even poured boiling water over them.
An Amnesty International statement said: "Numerous sources have also reported further acts of torture and other cruel, inhuman and degrading treatment of other migrant workers from Burma arrested by police in connection with the investigation.
According to reports, police officers poured boiling water over some of the Burmese migrant workers they were questioning. Others were also beaten and threatened."
Khunying Porntip Rojanasunan, a forensic expert, has blasted the police for failing to use a forensic pathologist from the start of the investigation.
“A case of two murdered people certainly needs a forensic physician,” she told the Bangkok Post.
The suspects are both Burmese migrants – a group that has previously been used as a scapegoat for crimes in Thailand. If convicted, they could face a death sentence.
The UK's Foreign and Commonwealth Office said it was keeping a close watch on the case and is concerned about the reports.
Thai police have come under domestic political pressure to solve the case, amid fears it could damage the tourism industry in the country. They deny the allegations of torture and say they have DNA and CCTV evidence to back up the confessions.
As the suspects were named, police chief Lieutenant General Jaktip Chaijinda said: "Today the case should be finished because we want to clear this case up as soon as possible so that our tourism industry can bounce back."
Richard Bennett, Amnesty International's Asia-Pacific programme director, said: "The Thai authorities must initiate an independent, effective and transparent investigation into mounting allegations of torture and other ill-treatment by police.
"The pressure to be seen to be solving an appalling crime that has garnered considerable attention should not result in the violation of rights, including to a fair trial.
"Authorities should provide protection from threats and acts of retaliation to anyone, regardless of their immigration status, reporting or speaking about torture or ill-treatment, and full redress to victims.
"They must also ensure that any alleged confession or information that has been coerced as a result of torture is not admitted as evidence in court, unless to prove that torture has been carried out."
A Foreign Office spokesman said: "We are concerned about the reports of allegations of mistreatment and expect these to be dealt with appropriately."
The spokesman said the UK government would not interfere, but expected the trail to be "conducted in a fair and transparent way."