A little housekeeping, for the record:
Yes, Iranian intelligence agents work out of the Iranian Embassy in Mexico City and yes, their primary collection target is the United States of America. Yes the Revolutionary Guard Qods Force maintains people as "illegal" (meaning not under diplomatic cover) agents in Mexico. They speak Spanish and they have access to competent cartel murderers (Chino Anthrax and crew being one of many). Questions still remain about the fumbled Arbabsiar Plot.
The Arbabsiar Plot and the Mexican Drug Cartels
Revisiting the plot
Shakuri is a member of the Iranian Revolutionary Guard Qods force, a foreign special operations element tasked with promoting the IRG's interests outside of Iran. Shakuri sent $49,000 to an undercover FBI bank account inside the United States to facilitate the assassination. USGOV was aware of the plot from the beginning, and while one might congratulate them for fine police work, one might also wonder whether or not Manssor Arbabsiar may have been entrapped (just a little bit).
Once the FBI took Arbabsiar into custody, they had him make consensual telephone calls to Iran (source DOJ)
"Arbabsiar made phone calls at the direction of law enforcement to [Gholam] Shakuri [a member of Qods Force] in Iran that were monitored. During these phone calls, Shakuri allegedly confirmed that Arbabsiar should move forward with the plot to murder the Ambassador and that he should accomplish the task as quickly as possible, stating on Oct. 5, 2011, '[j]ust do it quickly, it’s late.' "
Because the Obama Administration was under fire for Operation Fast and Furious, some have floated the opinion that the Arbabsiar plot was a smokescreen by USGOV to obscure the Congressional investigation into the misconduct of Attorney General Eric Holder and possibly of President Obama, himself.
I have no idea whether this is a USGOV smokescreen to obscure their Operation Fast and Furious fiasco or not because I have no first hand information. However, on the stupid scale, isn't 'walking' 2,000 firearms to the Sinaloa Federation Drug Cartel just about as goofy as Iranians working with Los Zetas proxies to assassinate a Saudi Ambassador in the US?
Why didn't the Iranians vet their "Mexican assassin" - an FBI operative - more carefully? You can chalk it up to amateurish Iranian work, but the Iranians aren't usually that stupid. That the Iranians were stupid doesn't mean that they didn't plot the work to be done. As they learned, a truck bomb in the basement of the World Trade Center didn't bring the tower down. It took Al Qaeda and jet liners filled with innocent passengers and fuel to make that happen.
The only thing that has kept the Islamic Republic from committing atrocities is their political calculus of the repercussions. With the Obama Administration's commitment to the Lloyd George school of diplomacy, what would those repercussions be? A harshly worded letter to the Supreme Leader of Iran wouldn't dent his armor or resolve.
The government’s complaint [.pdf] outlines an almost outlandish comedy of errors. Now we’re finding out that the administration itself had “expressed concern that the plot’s cartoonish quality would invite suspicions and conspiracy theories.”