When I began to research my book on Piero Gobetti, the precocious young anti-fascist journalist and early victim of Mussolini, the world in which he lived seemed very remote to me. I could relate little of the post-1918 anger and desperation – the obsession with borders and national grievance, the struggle to make ends meet in times of unemployment and rising inflation, the angry men convinced they had been dispossessed – to my own circumstances.

Far-right terrorist ‘manifestos’, like the one apparently published by one of the Christchurch shooters, are a kind of Rorschach test, inviting the reader to finish the job by finding meaning in the incoherent and contradictory ideas it contains. An act of mass murder is turned into a global spectacle by the use of real-time social media networks. Traditional media organisations and individuals online are drawn into repeating, arguing over and sharing the claims and images made by the perpetrator.

Pamela Mastropietro, an 18-year-old from Rome, left the rehab clinic where she’d been staying in the province of Macerata, in central Italy, on 29 January. Her dismembered corpse was discovered two days later, in two suitcases, in the countryside nearby. Innocent Oseghale, a 29-year-old Nigerian with an expired residency permit and a criminal record of drug dealing, was arrested almost immediately on suspicion of involvement in Mastropietro’s death.