It is damn near impossible to prove it beyond a reasonable doubt, though. For once, the government is the one who seemed to have the tinfoil hats on.
Even if it was certainly an Iranian op, and I do think that its possible that it was, Western Europe would give no shits, Canada and Britain would reluctantly back us with private statements of "Do we have to?", the Iranians would deny deny deny, the Saudis would be screaming for blood, Iraq, which we would be pulling out from at this point, would ignite in sectarian strife once more, and things would go apeshit in general.
Obama was thinking of his reelection. Foreign policy hawkishness was not popular at this point, and a military confrontation with Iran would not have a conclusive positive end, but rather would throw the Middle East into chaos it cannot afford with the Arab Spring going on, and radicalize Iran into more of a pariah state.
I am absolutely convinced that even if the government knew for a fact that Iran was responsible, and they succeeded, Obama would do nothing because it was politically expedient, and he would not be punished for it at the ballot box.