“More than 68 percent of the weapons recovered at Mexican crime scenes over a five-year period were traced to U.S. manufacturers or U.S. dealers who import firearms, according to statistics of the Bureau of Alcohol, Tobacco, Firearms and Explosives.
Between 2007 and 2011, Mexican law enforcement submitted 99,691requests to the ATF for tracing, and 68,161 of those firearms were determined to come from U.S. makers or were legally imported into the United States by federally licensed firearms dealers.”
Source:ATF: Most guns at Mexican crime scenes traced to US – El Paso Times