Lingering Question

I agree with the various points of view arguing that the Iranian-Zetas plot was not something that should keep anyone up at night (save perhaps the poor sap who, perhaps confusing some of the Zetas named Carlos with Carlos the Jackal, is now in jail), but this passage (from the Post) points to a question that I have not seen answered:

The alleged plan was foiled when Arbabsiar made contact with a man he believed was a drug-cartel member. Instead, it was an undercover informant for the U.S. Drug Enforcement Administration.

Are we sure he wasn't both? In other words, was it not a Zeta who informed the authorities, or was it someone the US had infiltrated? It doesn't seem to me to matter to much from the standpoint of Iranian capacity to carry out attacks in the US (the former case is actually more reassuring, because it indicates that even beyond the reach of the government, our ostensible enemies in the drug trade see their interests and ours as the same), but I am curious if the initial alert that there was some sort of attempt to hire Mexican hit men was the product of American or Mexican government agencies' proactive efforts, or it fell into their laps.