Justice reveals how Holder letter to Grassley came about
Story here. Apparently, when Sen. Grassley wrote Holder asking if guns were being "walked," the US Attorney for Arizona emailed Justice HQ that "Grassley's assertions regarding the Arizona investigation and the weapons recovered at the "murder scene are based on categorical falsehoods. I worry that ATF will take 8 months to answer this when they should be refuting its underlying accusations right now."
Since he had personal knowledge that guns were being walked, that would explain his sudden resignation. It's interesting that (1) Holder declined to state this when asked about the letter and (2) that it took this much prying to get the information out. I suspect the US Attorney has something to hold over HQ's head, or this would have been given up immediately. "I was lied to by a guy whom I demanded resign," is a quick and easy answer.
This would never have come to light but for a lot of persistence by Grassley and Issa, which tells you how easily an agency can lie to a senator and get away with it.
UPDATE: Unbelievable. The US Attorney for Arizona, Dennis K. Burke, was assuring HQ that Sen. Grassley was a "stooge for the gun lobby" and that he was "personally outraged by Senator Grassley’s falsehoods," and the mythical gun lobby was "lobbing this reckless despicable accusation..."
See that bus? ... be under it.
Hat tip to David Codrea.
ANOTHER update: Politico thinks Dennis Burke's career in AZ politics just capsized and sank. He noted "“No commentary by Grassley on the lax laws, nor greedy gun shop owners, nor careless straw purchasers..."