Why would a member of a Mexican drug cartel arm himself in the U.S.?  Quite simply because Mexican gun laws are much tougher than ours.  In Mexico, an individual can purchase a gun only from a licensed business and the purchase must be registered and approved by the Department of National Defense!  In the US, an individual in many states can buy a gun from an unlicensed seller without even a background check.  

But that's not all.  In states like Arizona and Texas where Mexican drug lords do business because of incredibly weak gun laws, traffickers can buy unlimited numbers of guns at one time and can purchase military-style assault weapons.  California is the only border state with Mexico that has laws strong enough to prevent major drug cartel purchases, but California's laws have no effect on criminals operating in neighboring border states.

Ample evidence for criminal export of guns can be found in the Brady Campaign's new report, EXPORTING GUN VIOLENCE (www.bradycampaign.org/xshare/pdf/reports/exporting-gun-violence.pdf).  Here's just one example of the cross-border drug trade from the Brady report:

Alan Rodriguez, 35, a struggling carpet-layer from the Dallas area, bought more
than 100 assault rifles, 9-mm handguns and other high-powered weapons
from U.S. gun dealers over several months, according to court records.
Authorities say traffickers gave him stacks of cash to buy the guns, with
marijuana laced in between the bills. He earned about $30 to $40 a gun,
according to court records. One of the pistols he bought in Dallas was used in a
cartel gunfight near Reynosa, Mexico, in which two federal police officers were
shot. In 2006, Rodriguez was sentenced to 5 ½ years in prison.

What we need to recognize is that the same US gun laws -- or lack of gun laws -- that wreak havoc in Mexico also wreak havoc in the US.  Again, as one example, the recent murder of four policement in Oakland involved an assault weapon that, while banned for sale in California, was likely transported from a neighboring state that allows the sale of assault weapons.

While we in California work hard to maintain and improve our gun laws, we are constantly reminded, now even by Mexico, that guns laws in other states and nationally are completely inadequate.  Mexico's Attorney General correctly called American gun laws "absurd."  We need national and international solutions to a national problem.