Meanwhile, Ezra Klein notes that Michael Gordon doesn't appear to have actually seen the evidence for Iranian complicity in this EFP business. Rather, "American intelligence says that its report of Iranian involvement is based on a technical analysis of exploded and captured devices, interrogations of Shiite militants, the interdiction of trucks near Iran’s border with Iraq and parallels between the use of the weapons in Iran and in southern Lebanon by Hezbollah."
This, of course, raises the perennial question of what kind of intelligence a country that's decided to deploy systematic torture as an interrogation method is actually getting. Were the militants handed over to some sub-agency charged with assembling a dossier on Iranian meddling in Iraq and then tortured until they confessed to getting Iranian help? Presumably if you let me torture them until they admit that the weapons have nothing to do with Iran, my interrogation would produce that result.