Almost immediately after the Justice Department announced a shake-up of the officials who oversaw ATF’s ill-begotten “Operation Fast and Furious,” Rep. Darrell Issa (R-Calif.) and Sen. Chuck Grassley (R-Iowa) signaled they wouldn’t let the reassignment of acting ATF director Kenneth Melson slow down their investigation of the questionable program.

Two days later, they’ve already made good on that promise. Today, they sent a letter to Ann Scheel, the acting attorney general in Phoenix, basically putting the Arizona district office on notice and demanding e-mails, memos, notes and other documents from six top officials, including Scheel and ousted former U.S. Attorney Dennis Burke.

“The level of involvement of the United States Attorney’s Office for the District of Arizona in the genesis and implementation of this case is striking,” the letter states. It continues:

Operation Fast and Furious was a prosecutor-led Organized Crime Drug Enforcement Task Force (OCDETF) Strike Force case. The congressional investigation has revealed that your office, and specifically Assistant United States Attorney (AUSA) Emory Hurley, played an integral role in the day-to-day, tactical management of the case. In fact, Mr. Hurley served as a prosecutor on this case until very recently.

Witnesses have reported that AUSA Hurley may have stifled ATF agents’ attempts to interdict weapons on numerous occasions. Many ATF agents working on Operation Fast and Furious were under the impression that even some of the most basic law enforcement techniques typically used to interdict weapons required the explicit approval of your office, specifically from AUSA Hurley. It is our understanding that this approval was withheld on numerous occasions. It is unclear why all available tools, such as civil forfeitures and seizure warrants, were not used in this case to prevent illegally purchased guns from being trafficked to Mexican drug cartels and other criminals. We have further been informed that AUSA Hurley improperly instructed ATF agents that they needed to meet unnecessarily strict evidentiary standards merely in order to temporarily detain or speak with suspects.

It is essential for Congress to fully understand your office’s role in Operation Fast and Furious. … In addition, it is imperative that the Committee have an opportunity to discuss the facts above with individuals in your office who are familiar with the details of this operation. It is not our intention to second guess day-to-day decisions of your staff, but rather to make sense of them. The Attorney General has said that “letting guns walk is not something that is acceptable.  … We cannot have a situation where guns are allowed to walk, and I’ve made that clear to the United States Attorneys as well as the agents in charge of various ATF offices.” Operation Fast and Furious is unique in that guns were allowed to walk with the apparent knowledge of, and authorization by, officials in your office.

Whew! That letter should make it perfectly clear. If AG Eric Holder seriously thought shuffling the players would shush the investigation, he should think again. Issa and Grassley won’t let up until they understand why anyone ever thought it was a good idea to allow straw purchasers to buy illegal weapons, knowing full well that the weapons would end up in the hands of Mexican drug lords and that ATF’s ability to track the weapons would be minimal-to-nonexistent. That AUSA Hurley apparently made it unnecessarily difficult for ATF officials who tried to interdict the weapons to do that job is even more mystifying and rightly investigated at greater length. Go Team Issa-Grassley, go!