We do not need any terrorist at all, thick or even highly intelligent.
But if this is of any help?
*** 'It may have been that they were on a test run,' said a source close to the case, who added: 'There was nobody in the car, and the cannisters were not connected to any detonator or explosives.' ***
Which brings to mind the IRA phrase following the Brighton bombing about them being unlucky once and the security services have to be lucky all the time.