Chum. An appropriate word, considering the US walked weapons, under the observation of the US government, at the scenes of multiple homicides. And with many more guns still out there, the chum--as you say--will continue to spread it's rotten and bloody scent in the water. Someone either screwed up really, really, badly, or criminally assisted these drug lords in the acquisition of weapons. The former is the most likely, in my opinion.
Either way, this is a huge problem and an investigation was/is absolutely justified. Unfortunately, Holder's earlier testimony seems to be contradicted by emails. Take note, the link I started this off with does not take one to the dreaded "FAUX NEWS."