[Ed. – Who could have possibly done it? It’s a mystery.]
For now we don’t know who was responsible for the attack, nor what the motive was.
However, we do know that the use of vehicles to drive into civilians is a mode of attack hugely difficult to stop.
Atrocities involving vehicle attacks have been carried out in France, Germany and Britain. Such vehicle attacks generally require very little planning, and no wider network, leaving little or no opportunity for the authorities to detect and stop them.
Las Ramblas was full of people, is largely or wholly open, with few obstacles to block the path of any vehicle.
Britain suffered vehicle attacks by Islamist terrorists in Westminster in March and London Bridge in June. In London Bridge the van was rented hours before the attack with reconnaissance of the area where the atrocity took place carried out minutes before.
Options to make a vehicle attack harder include making renting vehicles harder and placing barriers to limit how far an attacker could drive as they mow civilians down.