Gunwalking, or "letting guns walk", was a tactic used by the Arizona U.S. Attorney's Office and the Arizona Field Office of the United States Bureau of Alcohol, Tobacco, Firearms and Explosives, which ran a series of sting operations between 2006 and 2011 in the Tucson and Phoenix area where the ATF "purposely allowed licensed firearms dealers to sell weapons to illegal straw buyers, hoping to track the guns to Mexican drug cartel leaders and arrest them" - however as of October 2011, none of the targeted high-level cartel figures had been arrested. Wikipedia