"[T]he Office issued more than 2,800 subpoenas under the auspices of a grand jury sitting in the District of Columbia; executed nearly 500 search-and-seizure warrants; obtained more than 230 orders for communications records... obtained almost 50 orders authorizing use of s; made 13 requests to foreign governments pursuant to Mutual Legal Assistance Treaties; and interviewed approximately 500 witnesses, including almost 80 before a grand jury."