Third alternative was that the guys had run out of real explosives and thought that they might get some kind of effect by just blowing up the triggers.

Now that is something I find really unlikely. Chances are that at least one of them was british-educated like last time and not some camel-herder and thus would know better than thinking that. Having said that, people doing this sort of stuff are clearly fucked up in the head, so anything's possible. But still... naaaaaaaaaaaaah. Noone's that stupid.