I have no idea who is behind the attacks. If it turns out to be Hezbollah and/or Iran, that will not shock me: after all, if it is perceived that you have sent hit squads onto a country's soil to murder their nuclear scientists, it's likely that the targeted nation will want to respond with violence of their own.
A simple statement of understanding rather than any kind of justification? Read it as you will; for my part I'm not so sure - for reasons I'd set out here, some time before, in commenting on an earlier piece of Greenwald's of similar tendency. In any case, at the Guardian he's going to fit right in.