Is the US to blame for a massacre in Mexico?

In March 2011, dozens - maybe hundreds - of people in Allende, Mexico were kidnapped and murdered one night by the Zetas drug cartel. Survivors say no one came to help. The next morning, construction equipment rolled into the town, which is near the Texas border, and destroyed businesses and homes. Allende still looks like a war zone. All of this had a lot to do with American law enforcement gone wrong.