Two Burmese migrants accused of murdering two British backpackers in Thailand claim they were told they would "disappear" if they did not confess to the killings.
Hannah Witheridge, 23, from Hembsy, Norfolk, and David Miller, 24, from Jersey, were found dead on the island of Koh Tao on September 15 last year.
Burmese migrants Zaw Lin and Wai Phyo have been on trial for murder after denying their involvement.
Both defendants, aged 22, initially confessed to the killings but later retracted these statements, telling the court they had been tortured. Police have denied they tortured the accused.
Andy Hall, a British advisor to the defence team, has given evidence about the alleged torture to their trial in Koh Samui.
He told the Press Association that both men claimed they were subjected to mental and physical torture for up to eight hours after their arrests, while Wai Phyo says he was also sexually abused.
Mr Hall said: "They were told that if they did not confess they would simply disappear - they would be set on fire or their limbs would be cut off and sunk at sea so nobody would ever find them.
"The police told them 'you have a choice, you can either die or confess and spend a few years in prison'.
"They were terrified and did not know what was going on."
Wai Phyo claims he was stripped naked and photographed as his genitals were flicked and pulled in front of 20 police officers.
"He was sexually abused in the most humiliating way because he was holding out and taking longer to confess," Mr Hall said.
"It took him some time to open up about this as he is very shy and gets very upset when he talks about it."
Both men claimed they were beaten repeatedly and Zaw Lin says he passed out after being suffocated.
Mr Hall added: "He says officers placed a plastic bag over his head and he was forced to bite through it in order to breathe.
"A photo of Zaw Lin's beaten and bruised face was showed to Wai Phyo and that is when he decided to confess.
"We only have their account of what happened because the police deny it but, when I speak to them, it is quite clear they are utterly humiliated by this."
Post-mortem examinations showed that the young backpackers, who had met on the island while staying at the same hotel, both suffered severe head wounds and that Miss Witheridge had been raped.
Prosecutors say the DNA evidence links the two men to the killings but the trial heard that a garden hoe alleged to have been used in the killings carried the DNA of two men - but there was no trace of either defendant.
Mr Hall said: "The DNA evidence is absolutely central to this case and has been completely discredited in court."
The court is due to hear closing statements from the defence and prosecution on October 26 before delivering its verdict on December 24.