i know you're basque so i'm guessing you have experienced in a more familiar basis what terrorism can do.
yet, i don't see this guy as a terrorist. he didnt mean to harm others, just property in the middle of the night, when no-one is watching and therefore no-one is there to panic or feel, well, terror.
in any case, violence has been at the root of virtually every major change in the history of mankind. sometimes it is necessary to shake things up a bit in order to advance.
What if there was a night watchman there? what if there was a security upgrade going out at the bank during the night and someone was working there?
The issue I have with this is that there were far too many variables involved, he couldn't guaranteed he wasn't going to hurt people and for the non-watching part, where did the people who helped him coming from? nowhere?
If he wanted to make a statement instead of a bomb why didn't he think of something else to break the crystals of the bank and simply run away? it's the same principle, just far less dangerous.
When I was a teenager I knew a guy through a friend, he seemed to be a "normal" person, didn't really get into much trouble, I wasn't exactly friends with him but I had exchanged more than a few words with him, gone to parties, etc.
We all started uni and after a while I kinda lost track of the guy.
Next thing I knew, he had blown himself to pieces in France creating bombs for ETA.
No matter how careful you are, when you play with explosives, someone is bound to get hurt and that's why I can't have sympathy for this guy, if you play with fire, you will get burnt. It's a law of life.