The senselessness and random nature of mass shootings adds to their horror.

When children at school or teenagers at the cinema are killed and maimed by someone who might be a neighbour, normality is ripped apart.

The latest toll of 12 dead and 38 injured at a cinema showing the new Batman film in Aurora, Colorado, must now be added to the awful, lengthening litany of multiple killings. On this side of the Atlantic the two most shockingly memorable incidents are the mowing down of 16 five-year-olds and their teacher at a school gym in Dunblane in 1996 and last summer's massacre of 69 people at a youth camp on an idyllic Norwegian island. In the US there is an average of 24 cases a year.

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