In 2007-2008, according to ATF Special Agent William Newell, Mexico submitted 11,000 guns to the ATF for tracing. Close to 6,000 were successfully traced -- and of those, 90 percent -- 5,114 to be exact, according to testimony in Congress by William Hoover -- were found to have come from the U.S.
But in those same two years, according to the Mexican government, 29,000 guns were recovered at crime scenes.
In other words, 68 percent of the guns that were recovered were never submitted for tracing. And when you weed out the roughly 6,000 guns that could not be traced from the remaining 32 percent, it means 83 percent of the guns found at crime scenes in Mexico could not be traced to the U.S.