A British-born man who was a member of a team of ISIS killers in Syria nicknamed "The Beatles" pleaded guilty to criminal charges in a US federal court on Thursday.
Alexanda Kotey is one of two ISIS members who were held in Iraq by the American military before being flown to the US in 2020 to face trial on terrorism charges.
Kotey pleaded guilty to eight charges in a US District Court in Alexandria, Virginia.
Court records show Kotey faced charges that included hostage-taking resulting in death and conspiracy to provide material support to terrorists.
Another charge included conspiracy to murder American citizens outside of the US.
Kotey, who was stripped of his British citizenship, was reportedly involved in abducting American, European and Japanese citizens in Syria from 2012 to 2015.
It is claimed he belonged to the four-member ISIS cell known as "The Beatles" because of their British accents.
They are accused of detaining or killing several western captives, including US journalists James Foley and Steven Sotloff, and aid workers Kayla Mueller and Peter Kassig.
Under the agreement, he will serve 15 years in jail in the United States and then will be extradited to the United Kingdom, where he also faces charges of kidnapping and murdering hostages.
By admitting his guilt, he waived his right to a trial and faces several life sentences without the right to early release.
The families of the four American victims were present in the courtroom. Prosecutor Dennis Fitzpatrick said they had agreed with the change in defense strategy.
James Foley's mother, Diane, delivering remarks outside the courthouse, called on President Joe Biden, lawmakers and "all Americans to demand that our country protect and assist any innocent US national held hostage or wrongfully detained abroad."
She extended the thanks of the families of the four American victims to the Justice Department and the prosecution team "that has brought such a strong case for [Kotey's] direct culpability".
The cell reportedly took part in graphic ISIS videos posted online that showed foreign hostages being beheaded.
A 24-page indictment includes a list of tortures Kotey and the other Beatles are accused of inflicting on hostages, including electric shocks with a Taser, forcing hostages to fight each other, 20-minute beatings with sticks and waterboarding.
Kotey could face life in prison.
The US has advised British authorities that American prosecutors will not seek the death penalty.
Also extradited alongside Kotey was El Shafee Elsheikh, a Sudanese-born British resident, who is facing the same eight charges. The court docket showed charges against Mr Elsheikh are still pending.