The power to shock

It is extraordinary because it is something entirely outside our experience.

You don't expect to turn on the evening news to see a man, with blood-stained hands, standing on a street in London in front of the body of the man he has allegedly just killed.

The mobile phone footage, obtained by ITV News, already defines the horrifying killing of a young soldier in Woolwich. 

Soon this breathtaking footage was on constant repeat, a horrifying loop labelled Breaking News.

It appeared on screens around the world, and by the following morning was on the front pages of most British newspapers.

And there, in the background, the body of a murdered man.

Hundreds of people have already complained, to ITV and its regulator Ofcom, about the decision to screen the footage.

Some object on grounds of taste, others say it provides the very publicity the alleged killers sought.

But the decision to broadcast and publish these images has also been defended.

Writing for the Guardian, Roy Greenslade says: "pictures and film clips of the incident were across social media within minutes. Newspapers (and TV) would have looked completely daft to ignore what was already in the public domain."

But mainstream newspapers and ITV news bulletins are a different world from twitter and facebook. TV news comes into your home, newspaper front pages scream out at you from corner shops and supermarkets.

To defend the use of shocking material by arguing "it's already available online" puts you on a rather slippery slope. Videos of murder, torture and child abuse are all available online - but this doesn't mean they should be broadcast just before Emmerdale, or piled up next to a fridge full of sandwiches.

But these images were keenly gobbled up, and endlessly repeated, to keep rolling news rolling.

The killing in Woolwich highlights one of the biggest problems facing 24-hour news.

The culture demands you stay with a major breaking story, even when there is nothing else to say. New viewers will be joining you all the time, desperate for more information. But you have nothing new to give.

So instead you replay the same images, again and again, and remind viewers of the timeline of tragedy, and you desperately try to conceal the fact that you are saying nothing you hadn't said two hours earlier.

Could this endless repetition of the shocking be what makes us more immune to its power?

We now inhabit a culture where journalists know no more about a breaking story than the audience.

Through tweets and mobile phone video, the viewers have become part of the news cycle.

This can have huge advantages - there may not be a camera crew at a news event, but there'll almost certainly be someone with a mobile.

People know more now about the nuts and bolts of politics, business and the courts than they ever did before.

But there's little room for context, for considered reporting. Journalists and viewers are in a process of mutual learning, in which we're only ever a half-step ahead of the audience.

News is always Breaking News on Sky (and to a lesser extent on the BBC). Those bright red and yellow banners across the bottom of our screens appear so often, we barely notice them anymore.

Until something shocks us out of that complacency. Like the sight of a man with blood-stained hands, holding a machete a few yards away from a young man's body.