 During Operation Fast and Furious, the largest "gunwalking" probe, the ATF monitored the sale of about 2,000 firearms, of which only 710 were recovered .A number of straw purchasers have been arrested and indicted; however, as of October 2011, none of the targeted high-level cartel figures had been arrested.Guns tracked by the ATF have been found at crime scenes on both sides of the Mexico–United States border, and the scene where United States Border Patrol Agent Brian Terry was killed in December 2010.