The challenge for police and security services is that low-tech attacks - involving knives or vehicles - and often carried out by 
lone actors can be hard to spot in advance since they involve relatively little preparation and communication.

But in the wake of previous incidents in both the UK and other countries, police have been prepared for this kind of incident 
and seem to have been fast to intervene, taking few chances, although members of the public were also involved in 
restraining the individual.