If this was a clinically-planned attack, years in the making and masterminded by some ruthless organisation, then surely it would be less - please excuse the word but it gets across what I mean - amateurish? A criminal with convictions like that would surely be able to get hold of a gun, perhaps even some sort of automatic weapon? Surely he'd take a heavier, sturdier car - perhaps a lorry, perhaps with explosives in it, rather than a Hyundai i40? Perhaps he'd open fire with that weapon into a rock concert, or - if the location was important - then into the crowd opposite the London Eye on New Year's Eve?
Thankfully none of those things happened, and - tragic though it was for them - 'only' 4 were killed. But it could have been so much worse, very easily, and that is scary. You would hope that intelligence services would take down a group operating like that, but an individual could do so much more damage than this nutter caused. And the fact that it wasn't that much more 'clinical' does lend weight to the idea of it being a 'lone wolf', acting without much forethought.
