It's one of those images that has changed our sensibilities for good. The footage of the Woolwich suspect – as we have now absurdly to refer to him – wielding a meat cleaver, hands red with blood, discoursing with the owner of the mobile phone filming him, is beyond anything we have seen on British TV.
Yes, we've had blurry CCTV of murders and assaults, but usually they look more like ultrasound scans than useful evidence.
There have been the odd clips of horrific executions in sandy countries, but grim as they were, they were the Middle East, not middle England. Phan Thi Kim Phúc, the little naked burning girl in Vietnam, Ceaucescu's termination, Saddam's hanging, various butcheries in Rwanda and Burundi ... Dreadful imagery as they were, there was a firewall of sorts between us and them, between the viewer and the perpetrator, and, crucially, between everyone else and the victim or victims.
And there was, of course, the two soldiers murdered in Belfast, images caught by helicopter, so graphic that everyone was forced to pause for thought even in the midst of a series of atrocities.
There were those suicide videos recorded by the 9/11 and 7/7 bombers, but however compelling they were and however novel as far as such documents went, they were long after the event and the events were dreadful enough and had been their own commentary in the usual run of news coverage.
But really the Woolwich footage is very different. It came at us without context or preparation. For many people, it arrived before even the news about what had happened did. So there was no reassuring solemn-faced newscaster paving the way for what were to be distressing scenes or shocking images. You know, the way they used to do in the olden days.
The olden days of last week, before Wednesday.
Indeed, what there also wasn't was the sensible chap at the BBC who would scan the incoming camera footage from war zones and say 'Good Lord, we can't show that. Just get Simpson or Adie to describe it instead'. Or the way our much abused newspapers withhold the most shocking photographs from a public that still thinks it's entitled to vomit over their morning cereal.
No, this time, for the first time, the suspect was his own newscaster. Which saves some time, I suppose, given that on Newsnight on Friday, Anjem Choudary was given airtime to refuse to condemn the attack. In effect, the Woolwich suspect read the news to the nation, standing there, lecturing us, reassuring us, apologising to the ladies who had to witness what had just occurred on the street. Dressed in blood and gore.
In the aftermath, of course, there was much worrying about 'backlash', because it's easier to worry about that, 'backlash' being somehow familiar as a concept and controllable and easy to take a stand on, because it would at least have the merit of being predictable. Nothing about the meat cleaver was predictable.
There was much garbage too about why Woolwich was considered a 'terrorist' incident while the recent murder by stabbing of a Muslim man was just a 'crime' – but that was only another stratagem to shift the crisis onto other, safer bickering ground than the bizarre, frightening eruption of slaying which had taken place and for which no one, least of all the liberal wings, has an explanation. No Leveson inquiry for this one, peeps. You're on your own now.
And the emergency is still under way. One man was arrested on the premises of the BBC in London after giving a pre-recorded interview, again to Newsnight, during which he made unsubstantiated, uncorroborated and indeed unverifiable claims about his friend, the suspect, having been harassed by MI5.
With its now commonplace misjudgment of mood, the BBC repeated his claims for days. Moreover, and incredibly, the BBC had managed to find someone who would be arrested for terrorist-related matters actually not connected to the Woolwich attack! Other arrests took place over the weekend and there is talk of COBRA meetings and security reviews and, strangely, of the PM going off on his hols.
It's no mystery, though. In very obvious ways, Woolwich has set a new paradigm of terror. You don't need to raise an army any more. You don't need training camps in Pakistan to make lean killers out of plump western Muslims. Even half a dozen backpackers, in fact, is too many.
Now, all you need is a hatchet and a mobile.