He has not been directly implicated in the killings, but his participation in — and knowledge about — numerous kidnapping, ransom and murder plots was enough to secure a conviction under the law, prosecutors argued.
For years, American investigators suspected that there were a total of four Beatles who participated in the kidnapping and ransom scheme: Mr. Kotey, Mr. Elsheikh, Mohammed Emwazi, also known as Jihadi John, and Aine Davis.
But earlier this year, an F.B.I. agent testified during Mr. Elsheikh’s trial that there were only three main members of the group, casting doubt on Mr. Davis’s involvement in the ransom, torture and killing of the hostages. In 2017, a Turkish court convicted Mr. Davis, who was born in London, of being a member of the Islamic State. He was recently released from a Turkish prison and is likely to be deported back to Britain, where he could face terrorism charges.
Prosecutors in Northern Virginia have secured a handful of high-profile convictions in Islamic State-related cases, including that of Mr. Elsheikh and Mr. Kotey; Mohammed Khalifa, a Saudi-born Canadian, who was part of the Islamic State’s Ministry of Media, which was responsible for publicizing the beheading of Mr. Foley; and Allison Fluke-Ekren, an American woman from Kansas, who commanded a battalion of female fighters for the Islamic State.
Mr. Elsheikh, Mr. Kotey and Mr. Khalifa were sentenced to life in prison. Ms. Fluke-Ekren awaits sentencing after pleading guilty in June to a terrorism charge.
The British extremists repeatedly beat the hostages they kept imprisoned in Raqqa, Syria, which the Islamic State claimed as its capital at the time, according to prosecutors. They subjected their prisoners to abuses such as waterboarding, mock executions, painful stress positions, food deprivation, chokeholds that caused blackouts, electric shocks and beatings that lasted 20 minutes or longer.