Ms Mueller’s mother Marsha Mueller, of Arizona, told the court how she would receive emails from her captors, believed to be the Beatles, with demands for her release.

They demanded five million euros or the exchange of Aafia Siddiqui, a Pakistani neuroscientist who was serving a federal sentence in the US who has long been a cause célèbre in the terrorist world.

Ms Mueller was held hostage for over a year before it is thought she was given to Islamic State leader Abu Bakr al-Baghdadi, who reportedly raped and tortured her.

“Our family is not very wealthy, we are on our own,” said a tearful Mrs Mueller as she read an email sent to the captors pleading for her life.

The parents also sent a video addressing Baghdadi directly. Wearing a black veil over her head, Mrs Mueller said: “I am coming to you with a mother’s heart, I ask you for mercy. Kayla is not your enemy.”

In January 2015, the Muellers were emailed a photograph of their daughter’s dead body from an account belonging to the captors, who claimed she had been killed in a US-led coalition air strike. That account has since been challenged.

The court then heard from Marcos Marginitez, a Spanish former hostage, who testified that the Beatles were far more brutal than French, Belgian and Syrian guards in the IS prisons.

“The French guards were nice, cool compared to the British guys. (The Beatles) were very, very nasty,” he said. “Our conditions always changed immediately when they arrived. 

“We were not allowed to look them in the eye and had to kneel with our hands on the wall whenever they were there.

“They knew how to inflict the most pain.

“And they enjoyed it.”

The trial continues.