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.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.
—Rangel Sostmann, ITESM Campus Rector
With politics hopefully out of the way, let's look at the homicide data with a seasonal decomposition by loess:
Since homicides and homicides with firearm can rise at the same time because the overall level of violence in society is increasing, say because of land reform or election disputes, we should also look at how the proportion of homicides with firearm has changed in Mexico:
Now just the municipalities that border the United States:
Now, let's look at the big border cities:
But before we conclude that it was due to the assault weapons ban we have to take into account that "La Barbie", working for the Sinaloa Cartel, was trying to take over the drug trafficking routes of Nuevo Laredo after the capture of Osiel Cárdenas, the leader of the Gulf Cartel, in March 2003. And that as a consequence of the violence Vicente Fox started Operation Secure Mexico in June 2005 and sent troops to Nuevo Laredo:
Now let's look at the proportion of homicides by firearm in each of the states of Mexico and the Federal District. I used the strucchange package to help visualize the breakpoints (even though it's not quite correct to run a linear regression on the data that's what I used):
Of all the states I have to say that only Nuevo León and Chihuahua look especially interesting:
Supposedly after "El Chapo" Guzmán escaped from prison he began to rebuild his drug empire and sometime thereafter entered into a non-aggression pact with the Juárez Cartel, but on Sep 11, 2004, he ended the alliance by killing the brother of the leader of the Juarez Cartel, since neither the proportion or the number of homicides committed with a firearm changed in Ciudad Juárez, my guess is that the breaking of the pact had more to do with the rise in violence than the assault weapon ban.
Nuevo León also experienced a rise in firearm violence:
conventional wisdom that the availability of firearms increases suicides. This, of course, doesn't concern the effect of expiration of the ban on assault weapons so I'll leave it at that.
Before we conclude that the assault weapon ban affected Mexico we need a plausible mechanism for how assault weapons would benefit the drug cartels and clear up some confusions and misunderstandings regarding guns:
- 90% of the guns in Mexico come from the US: Of those traced, about 90% came from the US. The keyword being traced. This isn't all guns that were confiscated in Mexico, not even a random sample, but a highly biased one. For example, according to GAO, 25% percent of traced guns were assault weapons, while according to the Mexican government 50% of seized guns were assault weapons. So it would be mistaken to draw inferences about where the total percentage of guns come from. However, given that thousands of guns have been traced to the US, it would be correct to say that the United States is one of the main suppliers of guns to Mexico.
- Assault Weapons are "Military Grade": None of the assault weapons for sale to civilians in the United States are of military grade and with the exception of some collector items they are all semiautomatic. They deliver one round each time you pull the trigger. In a fully automatic weapon many bullets can be fired with one trigger press.
- "Cop Killer" Guns: Some bullets can pass through body armor; however, they are not for sale to civilians. For some reason drug dealers took to calling the guns that can fire this kind of bullet "Cop Killers," even if they can only load them with regular bullets.
During the period in which the Assault Weapon Ban was in effect, the sale of any newly manufactured gun that met any of the following characteristics was prohibited:
- Folding stock
- Pistol grip
- Bayonet mount
- Flash suppressor
- Guns specifically mentioned in the ban
In response to the ban, firearm manufacturers quickly retooled their guns so that they didn't meet the law's definition of assault weapon, and most of the banned features don't strike as particularly important. For example, I bet most guns smuggled to Mexico are disassembled and so a stock of any kind would be removed. And I've never heard of a cartel shootout that involved bayonet mounts.
However a recent analysis by the Texas Ranger's Border Security Operations Center highlights the importance of high capacity magazines.Unlike assault weapons, high-capacity magazines, which are used with many guns, have been selling briskly since the ban ended because prices have dropped considerably.
—The New York Times
It is very common to find live ammunition rounds strewn on the ground after drug cartel shootouts (examples: 1 2 3), reloading a gun when other people are shooting at you is not an easy task and cheap large capacity magazines are an advantage during long shootouts, like the ones that occured in Nuevo Laredo when "La Barbie" was trying to take it over from the Gulf Cartel. This would be one plausible mechanism through which drug cartels could have benefited from the expiration of the ban.
It's also a good idea to put the size of the effect (if indeed there was one) in the context of the drug war. Clearly they are separate processes:
chart comparing it to other border cities, you can see how it stands out in 2005 and 2006. During 2010, in Tamaulipas there were 338 drug related homicides during the first half of the year according to the Reforma newspaper, during all of 2005 there were a total of 351 homicides (all kinds). I can only surmise that the whole state of Tamaulipas and Nuevo Laredo are much more violent now than in 2005, even if the difference is not quite as stark as in other regions of Mexico.
I modeled the effect of the assault ban as a Zero-Inflated Poisson regression model predicting the number of homicides that occurred daily in Nuevo Laredo from the time Osiel Cárdenas was captured to the time the army arrived. The model with a breakpoint ocurring at the time the assault weapon ban expired proved superior to one without a breakpoint.
I think it is much easier to visualize the size of the effect with weekly data:
But the capture of Osiel Cardenas occured more than a year before the violence started, the army arrived more than six months after the violence started, there's a plausible advantage to having cheap high capacity magazines, and the rise in homicides coinicided with the expiration of the ban. I can only conclude that the expiration of the Assault Weapon Ban contributed to the violence in Nuevo Laredo with possible spillover effects in Nuevo León, and I've certainly updated my beliefs about the effect of the Assault Weapon Ban.
Clearly much work remains to be done, more complex models could be fitted to the data and I didn't answer all the questions of interest: I didn't perform a detailed analysis of the change in proportion of homicides by firearm in Nuevo Laredo or an analysis of what happened in Nuevo León, but given that "La Barbie", the guy in charge of taking over Nuevo Laredo, was caught on Monday, finding out the whether he took advantage of the expiration of the assault weapon ban should be a simple matter of asking him.
The code is here. (I used the excellent package Project Template to build the skeleton)