How do they know it was a suicide?
It's not like there are any body parts left if there was someone in the truck when the bomb detonated. First reports said the truck was simply parked by the fence. Then it was a car bomb. Then someone saw a truck driving along, but did not see it actually explode. We have independent reports of at least two explosions.
And consider the timing. Right in time to give the media something else to talk about besides the financial buggering that Bush is getting ready to do to every American taxpayer. And, of course, John "Bomb bomb Iran" McCain now has something to talk about in the debate with Obama other than the economy.