Paul Greengrass may be best known these days for his Bourne films — Supremacy, Ultimatum and, lately, Jason. But since his days in the TV documentary business, the English director has always had his eye trained on the real world.

His latest film, 22 July, about the 2011 Norway terror attacks in which 77 people died, made with a cast of Norwegian actors speaking English, follows in the tradition of Bloody Sunday, United 93 and, to an extent, Captain Phillips, by bringing clarity to an atrocity through pure force of cinematic technique.

The title makes the film sound self-contained: The car bombing and mass shooting carried out by the far-Right terrorist Anders Behring Breivik, and nothing more. But 22 July, which Greengrass adapted from the book One of Us by the Norwegian journalist Âsne Seierstad, is a patient, long-form piece, beginning 24 hours before the event and running all the way to Breivik's trial the following summer — and, with its magnificent, John Ford-like pair of final shots, a few cathartic steps beyond.

"Norway isn't on trial, Anders, you are," Breivik's lawyer, Geir Lippestad (Jon Øigarden), reminds his client (Anders Danielsen Lie) with barely concealed exasperation before his trial. "Are you sure about that?" Breivik smirks. The question is rhetorical — a sadist's preening bravado.

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But Greengrass's film goes on to show that Breivik has unwittingly stumbled on the truth.

Norway is being tested here: the country's ability to heal from these horrors depends on its capacity to manage them in line with liberal democratic principles — even though "justice" in this case seems to demand a swift and merciless counterstrike.

There is something deeply reassuring, and even radical, about a film in which evil is defeated by due process: "fighting this terror with the rule of law, not the barrel of a gun", as Prime Minister Jens Stoltenberg (Ola G Furuseth) puts it here.

Crucially, 22 July walks that walk itself. Its central characters are Breivik and Viljar Hanssen (Jonas Strand Gravli), one of the teenage survivors of the attack. But time is carved out for that defence lawyer's story, too, and the challenge of having to defend the indefensible for the not-immediately-apparent greater public good is thoughtfully explored.

Smartly, the massacre itself is dealt with in the first 35 minutes: Greengrass positions it in the narrative as something to brace for immediately, rather than anticipate.

We see Breivik preparing at his farm, alone, mixing explosives in cement mixers and kitchen blenders — while 150 miles south on Utøya, teenagers arrive at the Workers' Youth League summer camp, greeting friends, tramping up to the clubhouse.

The contrast is painful and multi-levelled: the teens are members of a progressive political youth movement, while angry, axe-grinding seclusion is the core of Breivik's racist creed.

The bomb attack and shooting are staged with an unsparing, unsensationalised frankness that has the compelling horror of front-line news footage. Individual details lodge in your mind like frames of reportage photography: outside the government building sheets of paper swirl like snow, while a businessman's body lies supine on the tarmac, limbs poking in the air like the claws of an upturned crab.

There are comparable moments on Utøya, too — not least when Viljar and his brother Torje (Isak Bakli Aglen) are separated and the former is shot, sustaining life-threatening wounds and giving the film its only explicitly gory moment.

But in terms of sheer blunt emotional force, the reunion in hospital between the unconscious, critically ill Viljar and his parents hits far harder. Played entirely without melodrama, the scene makes the attacks' full toll suddenly and heart-rendingly palpable — and was, for me, searingly hard to watch.

The film's determination to see its story through from multiple angles does result in a talky second half — not a problem in itself, although Viljar's recovery feels a little spelt-out. But it is less a true-life thriller than a kind of justice procedural — and a sharp, scouring work of moral seriousness from Greengrass.