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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The attack in Aurora has additional heartbreaking resonance because it took place so near to Columbine High School in Denver where, in 1999, two schoolboys killed 13 fellow students and injured 22 before shooting themselves. But that very repetition in the same geographical area highlights the polarisation of attitudes to gun control in the US.
The cinema killings will re-ignite calls for greater restrictions. But with opinion polls showing growing support for relaxing existing firearms law, it is a thorny political topic. That makes the call by Michael Bloomberg, the mayor of New York, for Barack Obama and Mitt Romney, the contestants for the presidency, to state what they are going to do about gun control a significant intervention. The fact that the latest attack took place in an enclosed space, in the dark, considerably undermines the argument that allowing citizens to carry a gun acts as a deterrent. Certainly no-one in the cinema shot the gunman. By contrast, in Britain the Dunblane shootings prompted strong public campaign to tighten gun law which resulted in a public inquiry and new legislation which banned almost all hand guns as well as improving security in schools.
The right to bear arms is such a totemic liberty to large numbers of Americans that politicians have been reluctant to campaign against it. James Holmes's motive is so far unknown but his lack of resistance to arrest suggests that, like the Norwegian killer Anders Breivik, the former medical student is intent on having his day in court. Mass killers are determined and difficult to stop but reducing the availability of weapons by restricting gun ownership must reduce the risk of shootings. It is to be hoped that Mayor Bloomberg and his 600 colleagues who are members of Mayors Against Illegal Guns have correctly identified a change in the mood of law-abiding US citizens. The horror of people, including young children, being shot in their seats while watching a superhero movie gives a chilling realisation to his words that gun crime is "killing people every day and it's not just an inner-city, east coast, west coast, big city phenomenon".
That reality cannot be ignored when the police are increasing their presence at other screenings of The Dark Knight Rises because of the risk of copycat crimes.