There is break all you can do to stop a nutcase with a car from ramming people short of, as Al suggested, martial law, curfews, pedestrianising
everywhere, big barriers installed at every kerbside etc
This time they hired a car, last time they stole one IIRC - but there's nothing to stop some guy the authorities don't know about and who has owned a car for the last ten years doing exactly the same thing. From the outside he'll look just like you and me - a normal person - inside he's a seething ball of rage and hatred and last time I checked we don't have a good way of detecting that.
For anyone suggesting a "policed" internet - I hope you are all looking forward to not being able to post here without a team of moderators reading everything and approving it.. and I hope TB has the funds to pay them!

Heck, forums like this might not even be allowed.