Counter-terrorism officers and security officials will doubtless fear that Woolwich fits into the category of crime that they can do little to thwart; random, lone-wolf, unsophisticated attacks, conducted by people who are not on the radar of the police or MI5.
The spectrum in which investigators will be working now is broad, and the characters within it unstable and unpredictable.
The Joint Terrorism Analysis Centre (JTAC), which includes members from MI5, MI6, GCHQ, the police and Ministry of Defence, will convene to decide what conclusions can be drawn from what has happened, even at this early stage.
If there is any suggestion that this attack might be the start of a wave, the threat level will be increased to either severe or the highest level, critical.MI5 and Scotland Yard have warned repeatedly about self-starters – people who have been radicalised in the UK, affected, perhaps, by the wars in Afghanistan and Iraq, or by Arab spring events, or by emerging al-Qaeda networks in Africa.