We were both right, so we both win!
For quite a while now, us knuckle-dragging neanderthal gun owners have been saying that most of the "crime guns" in Mexico come from the Mexican Government.
The anti-self-defense crowd has been saying that they come from holders of US Federal Firearms Licenses.
Turns out we're both right: Of the few Mexican crime guns that are run through the ATF's database, the majority do indeed come form a holder of an American FFL: The Mexican Government.
Of Arms and the Law: Sen. Glassley lights a fire under Operation GunWalker. Links to a letter sent from Senator Charles Glassley to Acting BATFE Director Melson in which he points out several inconsistencies (to put it mildly) in the ATF's story.