An Islamic State (IS) group suspect from Britain dubbed "The Beatles" pleaded guilty in a U.S. court Thursday to charges of conspiring to torture and murder hostages in Syria, including four Americans.

Alexanda Kotey admitted that he played a major role in the kidnapping and detention of American hostages. Some of the captives were beheaded, multiple reports disclosed.

Kotey is suspected of being a key member of an ISIS cell dubbed "The Beatles" involved in kidnappings and other heinous crimes in Syria and Iraq.

Fellow "Beatle" El Shafee Elsheikh, 32, entered a not guilty plea during a hearing last October. No details have been released yet on whether Elsheikh has reached a plea agreement with authorities.

A third Beatle, Mohammed Emwazi, who goes by the moniker "Jihadi John," died in a drone strike in 2015. A fourth terror suspect is serving a prison sentence in Turkey.

"Beatle" is a nickname given by the terror suspects' victims because of their accents. The group is notorious for torture and other brutality.

Kotey and Elsheikh are suspected of killing American journalists Steven Sotloff and James Foley, and relief aid workers Kayla Mueller and Peter Kassig.

The duo are also suspected of being involved in the deaths of other captives, including Alan Henning -- a UK taxi driver -- and Scottish relief volunteer David Haines, including two Japanese nationals.

Mueller, Foley, and Sotloff were beheaded and photos of Mueller's dead body were sent to her family through an email ISIS used to negotiate ransom with the captives' families, Assistant U.S. Attorney Dennis Fitzpatrick said in the plea proceeding.

Kotey pleaded guilty to all eight counts against him in U.S. District Court in Alexandria. The charges include hostage-taking resulting in death and torture and providing material support to a designated foreign terror organization from 2012 to 2015.

As part of his plea deal, Kotey must meet with the family members of the murdered captives. After he has served 15 years in the United States, the British government will be allowed to try him.

Even if Kotey gets a lesser sentence in a UK court, his agreement mandates him to be in jail for life.