Why hasn't Obama or Holder done anything about the ATF scandal?

ATF agents were told repeatedly by their supervisors to not cease any arms they confirmed to be heading towards Mexico going to the hands of Drug Cartels. The report says neither Holder or Obama knew or authorized this practice, and so far, not a single person has been fired, even though one of the weapons that was allowed to be smuggled into Mexico was used to kill a border patrol agent in January. Isn’t this more proof of the incompetence of the Obama Administration? This story has been out for over a month apparently, why hasn’t Obama or Holder asked the head of the ATF, Kenneth Melson, to resign?