It appears that some traces were deposited days before L's death on an airplane that flew between the UK and Russia. If it is improbable that L flew to Msocow and back to the UK at that time, this bit of evidence greatly strengthens the hypothesis that some bungler apart from L was doing the principal bungling.
It is conceivable that someone traveled with the polonium from Moscow to the UK at L's behest. Call this Bungler Hypothesis 1.1.
One wants to know if the traces of polononium might have been deposited as a result of trips to to the bathroom. In this event presumably a large amount of polonium 210 would not have to have been involved. But if such bodily secretions were the source of the traces at the 12 locations, L probably was not the source -- since he probably did not fly to Moscow and back. Or?