The men accused of the murder of two British tourists on the island of Koh Tao in Thailand have failed in a High Court bid in London to gain access to a confidential report prepared by the Metropolitan Police.
The report was prepared to reassure the victims' families about the investigation conducted by the Thai authorities into the deaths.
Burmese migrants Zaw Lin and Wai Phyo, both 22, deny killing David Miller, 24, from Jersey, and Hannah Witheridge, 23, from Great Yarmouth, Norfolk, in a trial that began last month and is still continuing.
The bodies were found at a beach on the popular tourist island in September last year.
Lawyers for the accused men, who could face the death sentence if found guilty, asked Mr Justice Green to order disclosure of the police report in the hope that it might help their defence.
Rejecting the application, the judge said: "There is nothing in the report which is exculpatory or would be of material assistance to the claimants in the operation of their defence in the course of the trial."
The judge said the matter had been dealt with as a matter of urgency as the prosecution had almost completed presenting its case and the accused would open their defence shortly.
He said: "The stakes are very high for both sides. For the claimants they could hardly be higher: life or death."
The application for disclosure had been brought under the 1998 Data Protection Act.
The judge said the case raised an important legal point about the extent to which police authorities, when co-operating with foreign police authorities, "must make the fruits of their labour available" to individuals whose personal data appears in police reports.
The Metropolitan Police argued they were entitled to refuse access because of the need for confidentiality during international co-operation between police forces, and a court order for disclosure would have "a very serious adverse effect" on future co-operative ventures.
Lawyers for the accused men said such an argument could not prevail in death penalty cases.
The judge said: "My ultimate conclusion is that there is nothing in the personal data which would be of any real value to the claimants."
The objections to disclosure raised by the police "are valid and, on the facts of the case, suffice to outweigh the claimants' otherwise strong interest in access".
The judge said he had made his decision feeling "very considerable unease" as he did not have a true "hands on" feel for the trial in Thailand. He said that doing "the best I could" had not been "a comfortable process".
He added: "I have not been assisted by the lack of evidence about the Thai proceedings or as to the evidence that has in fact been tendered by the prosecution or as to the main lines of defence".
Rosa Curling, of Leigh Day Solicitors, who acted for both accused men, said there would be no appeal.
Ms Curling said: "Our clients are disappointed not to be able to verify their data themselves.
"But they are reassured that at least a British judge has now looked at the information held by the Metropolitan Police, applying anxious scrutiny, and determined that it would not assist them in their ongoing proceedings in Thailand."
The legal charity Reprieve also expressed disappointment, and spokeswoman Zoe Bedford said: "Concerns about the conduct of the Thai investigation and the safety of any convictions resulting have been raised from the very beginning of this case, including by the Foreign Office.
"The defence team has not seen the information in the Metropolitan Police's possession - only the defence lawyers in Thailand are in a position to judge whether the information could be of assistance. It is disappointing that they have been denied this opportunity."