The brother of a British aid worker kidnapped and later killed by Daesh (ISIS) will testify against the remaining members of the group's 'Beatles', to support their prosecution in the US.
Mike Haines, whose brother David was beheaded on camera in September 2014, has given a statement to British police and said he is ready to travel to the US to testify in person, if necessary.
The two defendants, El Shafi El-Sheikh, 32, and Alexanda Kotey, 36, appeared in a US court via video link for the first time on Friday. Both claimed they were only responsible for sending emails demanding ransoms.
However, Haines, according to the Times, has crucial evidence that could undermine the defendants defence, as he claims the kidnappers never responded to his family's attempts to get in touch.
Instead, Haines now believes Daesh never planned to release British and Americans captives.
The only communication the Haines family received from David was delivered when a French hostage was released in 2014. The note, written on his kidnappers' behalf, demanded £136 million ($177 million) ransom.
The staggering sum is an amount which Haines told the Times he would never have been able to pay even "if every member of the family had sold everything".
Meanwhile, it also emerged on Sunday that the pair have managed to assemble a top legal team, which is expected to be funded by taxpayers.
The team includes lawyers that represented the perpetrators of 9/11, such as Edward MacMahon, who represented both Walid Bin Attash and Zacarias Moussaoui, who were both involved in planning the 2011 attacks.
The other two members were Mohammed Emwazi, who was known as 'Jihadi John', and Aine Lesley Davis. Emwazi was killed in a drone strike in 2015, while Davis was sentenced to seven years in prison in Turkey in 2017.
The pair, who were flown from Iraq to the US last week, could face life imprisonment in solitary confinement at a Colorado-based maximum-security prison, but will avoid the death penalty, even if it is imposed, because of a deal made in the UK.
Under the deal, the US has agreed not to hand down the death penalty, or not carry it out, in exchange for key evidence from the UK.