IS "Beatle" El Shafee Elsheikh has been found guilty of hostage-taking and conspiring to murder journalists and aid workers in Syria.
The 33-year-old former British national was found to be part of an Islamic State terrorist cell that operated in Iraq and Syria, and whose members were nicknamed "The Beatles" because of their UK accents.
He now faces up to a life sentence in prison.
The group caused outrage around the world after releasing videos of the executions of US journalists James Foley and Steven Sotloff.
US and British authorities say the IS Beatles were responsible for killing 27 people, including British volunteers David Haines and Alan Henning and American aid workers Kayla Mueller and Peter Kassig.
The group's ringleader Mohammed Emwazi, nicknamed Jihadi John, was killed in a 2015 drone strike, while a third member, Alexanda Kotey, was already serving time behind bars.
Another man, Aine Davis, currently in jail in Turkey, was not considered by the US Justice Department to be part of the cell.
Known For Their Cruelty
During opening statements, the court in Virginia heard how Elsheikh and his counterparts were "utterly terrifying" and held 26 Western hostages in a prison called "the desert".
Victims were subject to "unrelenting and unpredictable" abuse, prosecutors said, adding the perpetrators "seemed to enjoy beating" them.
They were given "dead legs" and placed in "stress positions" while being "threatened with murder", the jury was told.
The group were known for their cruelty, forcing prisoners to fight each other and making them sing song parodies.
Surviving hostages testified that the Beatles delighted themselves rewriting "Hotel California" as "Hotel Osama" and making them sing the refrain "You will never leave."
The guilty verdict came even though none of the surviving hostages could identify Elsheikh as one of their captors. Despite their distinctive accents, they always hid their faces behind masks and ordered hostages to avoid eye contact or risk a beating.
The surviving hostages were all European, with the Americans and British among them all killed.
Conviction Centred On Four American Deaths
The convictions on all eight counts in US District Court in Alexandria revolved around the deaths of four American hostages: James Foley, Steven Sotloff, Peter Kassig and Kayla Mueller.
All but Ms Mueller were executed in videotaped beheadings circulated online. Ms Mueller was forced into slavery and raped multiple times by Islamic State leader Abu Bakr al Baghdadi before she was killed.
Elsheikh, who was captured by the Kurdish-led Syrian Defence Forces in 2018, eventually confessed his role in the scheme to interrogators as well as media interviewers, acknowledging he helped collect email addresses and provided proof of life to the hostages' families as part of ransom negotiations.
Surviving witness Federico Motka recounted a time in the summer of 2013 when he and cellmate David Haines were put in a room with American hostage James Foley and British hostage John Cantlie for what they called a "Royal Rumble". The losers were told they'd be waterboarded.
Weak from hunger, two of the four passed out during the hour-long battle.
US Promise Not To Seek Death Penalty
Defence lawyers acknowledged that Elsheikh was a member of IS, but said prosecutors had failed to prove he was a Beatle. They cited a lack of clarity about which Beatle was which, and the confusion over whether there were three or four members of the cell.
However, prosecutors said it did not matter whether Elsheikh was "George" or "Ringo".
Kotey and Elsheikh were captured together in 2018 and brought to Virginia in 2020 to face trial after the US promised not to seek the death penalty.
Kotey pleaded guilty last year in a plea bargain that calls for a life sentence but leaves open the possibility that he could serve out his sentence in the UK after 15 years in America.