So the big press conference was purely a show, timed to derail Issa's subpoenas. The presser could have been held last week or next year or never. If anything, the big presser killed any other investigative work on the case. Holder just used the case like a Kleenex.
Yes it was stopped because the guy mistook an undercover DEA agent for A Mex. drug cartel guy. But they couldn’t announce anything back then. They had to play along to get more info & evidence.