Three words: statute of limitations.
True, but federal employees could lose their jobs and pensions regardless. In fact, that would likely be the max penalty, limitations or not.
R.I.C.O. (Racketeering Influenced Corrupt Organization) fits the bill there. Lay out the entire scheme. Ok to include indictable acts that predate the statute of limitations, Usually 5 years prior to the date of the indictment. Bring in criminal forfeiture and take the entire enterprise completely down.