Writer-director Jonathan Hacker’s documentary offers a chilling historical document, chronicling a closed but not entirely concluded chapter in the sprawling history of 21st-century terrorism. Drawing on the skills of several editors, Hacker and co weave together footage shot by both the Saudi Arabian security forces and several interrelated Al-Qaida cells who in the early 2000s pursued a campaign of suicide bombings and assassinations in and around Riyadh.

At times, an explanatory voiceover narration from that omnipresent British baritone of authority, Samuel West, (supplemented by interjections spoken by Tom Hollander representing the “voice of Jihad”) provides terse explanations. But otherwise there’s little to no editorialising to guide viewers’ reactions, unless you’re counting the ordering of the material or Chad Hobson’s delicate, haunting musical score.

So we’re left to draw our own conclusions about what strange forces of accident or design have drawn these young men together for such murderous purposes. Sometimes these gaggles of guys look like ordinary young men, joking with each other, having wheelbarrow races in the desert, practising somersaults … if you only took the Kalashnikovs and homemade explosives out of the frame. In one chilling sequence, little boys barely able to walk join the fun, their heads swathed in black balaclavas, their skills at drop and roll while armed praised by voices off. Talk about your banality of evil.

But as a film this is anything but banal, and operates as a potent reminder of the randomness, and casual cruelty of modern terrorism, the way it leeches out the humanity of victims and perpetrators on both sides. Those with an aversion to blood and guts should stay clear – there’s ample footage of smashed and shredded bodies, sights that become almost numbing after just 91 crisply told minutes, which says more about us and the compassion fatigue that gets us all.