With growing violence on the U.S.-Mexico border fueled by powerful drug cartels, officials from both countries have been repeating a shocking statistic to suggest this isn't just a Mexican problem. But Obama, Clinton and others have left out important qualifiers when citing the 90 percent statistic, which originates from the U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives. The agency doesn't have statistics for all weapons in Mexico, where gun sales are largely prohibited; it is based on only guns that the Mexican government sent to the ATF for tracing and that the ATF found were traceable.