we know. the issue is - how did it get there, did he travel to spain? how, if he was being tailed by the FBI?
Some other people in this thread said he had never been to Spain. But, just speculating now...what if he maybe gave someone a bag of money/valuables/papers/etc., perhaps to finance the operation, that they took to Spain, and then used to carry the materials to the trains?
There are all sorts of ways he can be implicated in this, even if he never went to Spain. Material support, you know?