The United States Bureau of Alcohol, Tobacco and Firearms (ATF) reported that over 60,000 guns were seized in Mexico and traced back to being sold in the United States between 2007 and 2011.
The number of guns seized each year is as follows:
2007: 11,842 firearms seized in Mexico and found to have been originally purchased in the United States.
2008: 21,035 firearms.
2009: 14,376 firearms.
2010: 6,404 firearms.
2011: 14,504 firearms.
All of the weapons sent to the ATF by Mexican authorities were believed to have been used in crimes. Many of the guns were found in the possession of drug cartel members.
Source: Associated Press, “US: Mexico seized 68,000 guns from US since 2006,” Miami Herald, April 26, 2012.