Maybe they're waiting for Osama or his right hand man to step forward and officially claim responsibility. Osama is kicking back somewhere and laughing his a** off and our buffoon president and the people that voted for him. Serial numbers on weapons LOL our government couldn't even keep track of the serial numbers our own missing weapons, Or the serial numbers of the hundreds of tons of One hundred dollar bills that are unaccounted for in Iraq. Or the social security numbers of dead veterans that they sent recall letters to serve in Iraq after they had already given their lives for their country. You are saying that they can keep track of Iranian serial numbers but all of the other important serial numbers were on the bottom of the BS list therefore the Bush administration can just forget and lose track of them.
If the Iranians were indeed providing weapons and personnel in Iraq doesn't the US have a adequate intelligence service to declare this as fact with solid proof? There is no solid proof. Bush just has to keep throwing crap against the wall in hopes that something sticks just like he did for his solid justifications for the Iraq war.