In an effort to obtain prosecutions of criminals higher up in the food chain, the ATF purposely allowed guns to be sold to intermediaries, then pass into Mexico where they were used in various crimes involving bandits and the drug cartel. The majority of the guns involved in this scheme remain at large.
This caught a little more than usual non-attention due to the slaying of U.S. Border Patrol Agent Brian Terry. Two of the weapons associated with this crime were traced to the ATF Fast and Furious operation which allowed those guns to pass into Mexico.
Whistle blowers within the ATF are expecting to be jobless due to having provided some of the information linked above. It’s worth a read.