In interviews, the two men, Alexanda Kotey and El Shafee Elsheikh, for the first time admitted their involvement in the captivity of Ms Mueller, an aid worker who was held captive and tortured and sexually abused before her death in 2015.
Kotey said: “She was alone in a room that no one would enter. ”
Elsheikh went into more detail saying, “I myself took an email from her,” meaning he got an email address that ISIS could use to request an email. ransom to the family. “She was in a big room, it was dark, and she was alone, and… she was very scared. ”
In an email reviewed by NBC News, ISIS asked the Muellers to pay € 5m (£ 4.55m) and threatened to send the family “a photo of Kayla’s corpse. If the demands were not met.
Kotey and Elsheikh are both being held by the US military in Iraq amid questions about how and when they will face justice.
US and UK officials have said the so-called Beatles were responsible for 27 murders, including the beheadings of Americans James Foley, Steven Sotloff and Peter Kassig, and UK aid workers David Haines and Alan Henning.
Families of US hostages murdered by ISIS told NBC News they are urging the Trump administration to bring them to trial in US civilian court.
“They horrified so many people so much,” said Marsha Mueller, Kayla’s mother.
“They must be brought here. They must be prosecuted. The other thing that is really important to me about this is that I need some information about Kayla. We know so little about what happened to him. ”
She added: “I think these two have more information than they share with us. And I believe we would know more if they were brought here. ”
“They admit they were there,” said Kayla’s father Carl Mueller.
“And of course, they won’t tell the dark side of the story. “
American families published an opinion piece in the Washington Post on Thursday, imploring the Department of Justice to bring the two men to the United States for prosecution.
While in captivity, Kayla was taken to live with a senior ISIS official and raped by former ISIS leader Abu Bakr al Baghdadi, US officials said.
Baghdadi committed suicide with a suicide vest while being pursued last fall by US commandos during a raid in northwestern Syria.
Kayla is believed to have died in 2015 in what IS called a Jordanian airstrike. How she was killed has never been confirmed.
In a 2018 BBC interview, Kotey and Elsheikh denied ever meeting Mueller.
“WHO? Elsheikh responded when asked if he had ever met Mueller.
“We haven’t met any foreign non-Muslims,” Kotey added.
In the new interviews, Kotey and Elsheikh sought to distance themselves from the torture and killings attributed to them as prison guards, calling themselves “liaisons” with the hostages. But each admitted having beaten captives and played a role in facilitating communication with their families in an attempt to obtain ransoms.
“I never denied that they were (sic) affected,” Kotey said of the hostages. As an example, he spoke of hitting a Danish captive in the chest to make a mark that would be visible in a photo that would be sent to his family.
Elsheikh and Kotey were captured in Syria in 2018 by the Kurdish-led Syrian Democratic Forces.
The Kurds turned them over to the US military and President Donald Trump was considering sending Kotey and Elsheikh to the US military prison at Guantanamo Bay, Cuba, NBC News reported.
U.S. officials told NBC News that the United States is determined to ensure that the two men are indicted in a U.S. courtroom and that efforts to bring them from Iraq continue.
That effort suffered a setback in March, when the British Supreme Court ruled that the UK could not share evidence with US prosecutors while the two men faced the death penalty.
A criminal court is the best place to find out the truth, said Chuck Rosenberg, former federal prosecutor and NBC News legal analyst.
“We have had great success in the federal courts of the United States in terrorism cases,” he said. “This is absolutely where they belong. Not in Guantanamo Bay, not in military courts, but in United States federal courts. ”
Former hostages who managed to break out of ISIS detention said the four “Beatles” members, who were given the nickname because of their British overtones, were cruel and sadistic kidnappers.
Mohammed Emmwazi, the black-clad terrorist known as Jihadi John who beheaded numerous hostages on camera, was vaporized by Hellfire missiles from a CIA drone in 2015. The Fourth Beatle, Aine Lesley Davis, was sentenced to seven and a half years in prison in Turkey in 2017.
According to a State Department account designating him as a terrorist, “Elsheikh would have earned a reputation for waterboarding, mock executions and crucifixions while serving as an ISIS jailer.”
The State Department said Kotey, as a prison guard, “was likely involved in the group’s executions and exceptionally cruel torture methods, including electronic shock and waterboarding.”
Both men have denied this in the new interviews.
“Everyone’s talking about the rights of these two Beatles,” Art and Shirley Sotloff said in a statement to NBC News.
“What about the rights of our children, Steven and Jim and Peter and Kayla? Don’t they have the right to do justice?