STRATFOR: Mexico’s Gun Supply and the 90 Percent Myth. “It has now become quite common to hear U.S. officials confidently assert that 90 percent of the weapons used by the Mexican drug cartels come from the United States. However, a close examination of the dynamics of the cartel wars in Mexico — and of how the oft-echoed 90 percent number was reached — clearly demonstrates that the number is more political rhetoric than empirical fact.”