BRITAIN on Tuesday handed to US authorities evidence related to two members of a Daesh (the Islamic State group) killing squad dubbed "the Beatles", after Washington assured it would not seek the death penalty during their trial.
The evidence regarding El Shafee Elsheikh and Alexanda Kotey "has now finally been transferred to the US", Home Secretary Priti Patel said on Twitter.
"I sincerely hope that justice for the victims and their families will now be served," she said.
A Home Office spokesman said Patel was "clear in her determination to deliver justice", and the "priority has always been to protect national security".
"We continue to work closely with international partners to ensure that those who have committed crimes in the name of Daesh are brought to justice," he added.
Relatives of two Britons killed by the Daesh squad welcomed a breakthrough that advances the US trial of two Londoners accused of their brutal deaths.
Taxi driver Alan Henning and former aircraft engineer David Haines, who had both gone to Syria to do aid work, were beheaded in 2014.
Their families the London High Court's ruling permitting the UK government to share evidence with US authorities about the suspects was a "huge result for us".
"We have only ever wanted to see these two men being held accountable and brought to justice through a fair trial for their alleged actions," they said in a statement released by the charity Hostage International.
Another of the squad's alleged victims was British photojournalist John Cantlie, who was kidnapped in Syria in 2012 and remains missing.
Cantlie's sister, Jessica Pocock, said the family was frustrated at the long legal wait.
"At times we felt absolutely desperate as to whether the legal system was ever going to be able to bring these two to justice -- wherever they may be," she told BBC radio.
"That was always terribly important to us to have a proper, fair trial. The families need nothing less than a fair trial."
Elsheikh and Kotey, who have been stripped of UK citizenship, are in the custody of US forces in Iraq.
The US wants to try them for the murder of journalists James Foley and Steven Sotloff, and aid worker Peter Kassig during 2014-2015.
Kotey and Elsheikh's four-member squad had been called "the Beatles" by their captives due to their English accents. They tortured and killed victims, and Daesh released videos of the deaths, including by beheading, for propaganda purposes.
The transfer of material intended to help the pair's prosecution came after Elsheikh's mother lost a legal challenge in London's High Court.
Maha Elgizouli's lawyers had told the court that Patel's decision to press on with the transfer breached Britain's Data Protection Act.
But the judges ruled that the home secretary was within her rights.
"The conclusion that, even if Mr Elsheikh could be prosecuted in England, it would still be necessary and proportionate to transfer the data to the US authorities remained a conclusion properly open to the secretary of state," the ruling said.
A two-year legal impasse concerning the suspects was broken last month when Attorney General Bill Barr said they would be spared execution if convicted after trial in the US.
But he warned that unless the British evidence was shared by October 15, Kotey and Elsheikh would be handed over for prosecution and possible execution in Iraq.
Barr's intervention put the onus on Patel to see if the British system could overcome the court challenge by Elsheikh's mother and share the evidence, said to be damning wiretaps, with US authorities.
The US Department of Justice welcomed Tuesday's court ruling in London and expressed gratitude to Britain for transferring the evidence.
"We remain committed to holding these defendants accountable and obtaining justice for the victims of their terrorist activity," it said in a statement.
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