How the expiration of the assault weapon ban affected Mexico

There has been a lot of attention paid to the role of US guns exacerbating the violence in Mexico. The assault-weapon ban expired on September 14, 2004, but with the recent spiraling of violence in Mexico the ban has attracted renewed attention. Just recently the Mexican President stood before the American Congress and blamed the assault weapon ban for the rising violence in Mexico, seemingly without proof. This post will try to clarify some of the issues surrounding the controversy.

I think it would be fair to say that the conventional wisdom by scholars who have studied the ban would be the one Christopher Koper, Daniel Woods and Jeffrey Roth stated: "We cannot clearly credit the ban with any of the nation’s recent drop in gun violence." In other words, the assault weapon ban had no significant effect—at least where the United States is concerned. And as far as I know there are no studies of the effect of the ban expiration on Mexico.

As is well known, gun control is politically charged issue, not only in the United States, but also in Mexico. For example, after two students died in a shootout between the army and cartel gunmen, the rector of what is arguably Mexico's best university stated:

For me [Rangel Sostmann] the solution is that Mexico and the United States must change their policies. And the policy right now is for the United States to send the money and weapons, and Mexico puts the dead and the drugs. And that ultimately is not going to work, it's not a question of driving the Army out, the problem is that you have to change the policies, in this case the United States policy.
—Rangel Sostmann, ITESM Campus Rector

Later an investigation by the National Human Rights Commission concluded that the army had used excessive force, impeded the investigation, planted weapons on the students, possibly tortured them for several minutes, and then shot them at point blank range. The day after the report was released, the ITESM bestowed upon the Secretary of Defense the "AdHonorem" award, given to persons whose works have contributed in an outstanding manner to the "the fight against injustice." As you can see gun control has become extremely politicized, to say the least.

With politics hopefully out of the way, let's look at the homicide data with a seasonal decomposition by loess:

As you can see from the charts there was an increase in the number of homicides and homicides with firearm that coincided with the expiration. The big drop at the start of 2007 was due to the military operations in Michoacan and Acapulco, and also to a temporary drop in the homicide rate of Mexico City (which had nothing to do with the drug war).

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