British Police secretly helped Thai authorities put two men on death row for the murder of Jerseyman David Miller, it's claimed.
An investigation has uncovered the National Crime Agency passed on information that was used in the trial of Zaw Lin and Wai Phyo, also known as Win Zaw Htun - the men convicted of killing Mr Miller and fellow traveller Hannah Witheridge.
The bodies of Mr Miller, and Hannah Witheridge were discovered bludgeoned to death on a Thai beach on the 15th of September 2014.
David from Jersey, and Hannah from Norfolk, were each travelling with friends in the island of Koh Tao, when they were brutally murdered. Postmortems showed they'd received violent blows to the head and Hannah had been raped.
The two Burmese migrant workers were found guilty and sentenced to death on Christmas Eve.
News agency Buzzfeed UK claims officers from the National Crime Agency were contacted by forces in Koh Tao in the days after the deaths and asked them to pass on the serial number of Mr Miller's missing phone.
The smashed phone was found on a property that linked the men to the crime and that evidence became a crucial part of their prosecution.
That level of co-operation is forbidden by the NCA, when working with countries that use capital punishment - unless they get written assurance the accused won't be sentenced to death or have ministerial permission.
Both the Foreign Office and Home Office in the UK refused to say whether or not they had allowed the action.
Thai police later made an official request to use the phone as part of the prosecution's case, but the NCA refused - due to the lack of death penatly assurance. By that point though, officers knew the phone was David's and used it as evidence regardless.
The National Crime Agency has told ITV News it would be 'inappropriate to comment substantively on an investigation conducted by the Thai authorities'.
Officers are allowed to pass on details in this way, without seeking assurances, but it must only be in 'exceptional circumstances', when British lives are at risk.
Authorities must also have a Minister's permission first.
In this case, the NCA said they were worried other British holiday-makers could be in danger and were worried about the quality of crime scene evidence.
At the time of the investigation, Metropolitan Police officers were sent over to Koh Tao to oversee. Due to the high risk of human right violations, officers were banned from being involved - because there was no written assurance the death penalty wouldn't be used.
Both Lin and Phyo are appealing their sentences and their team say they will take their case as far as the Supreme Court. They claim they were tortured into confessing and were framed by Thai Police.