In August 2014, a video appeared on YouTube showing a shaven-headed forty-year-old man kneeling in the sand, his orange jumpsuit flapping in the breeze. To his left, a black-clad figure in a mask jabs at the camera with a knife. Speaking in a London accent, the masked man – immediately dubbed ‘Jihadi John’ by the British media – harangues his audience with a speech boasting about the rise of Islamic State. The camera fades to black and the next sequence shows the man’s bloodied head placed neatly on his back.

The victim was James Foley, an American freelance journalist who, along with his British colleague John Cantlie, was kidnapped in Syria in November 2012. According to one survey, Americans paid more attention to the murder of Foley and Steven Sotloff, another US freelance journalist killed in a similar way two