OK, the Oversight Committee is beating on Holder unmercifully because it has been 13 months since they sent the first letter and he told them an investigation is underway and he still can't answer the question of who authorized the gunwalking.
Holder responds by saying it will take time "to build a case" to "arrest and prosecute." So essentially, Holder just promised Congress he was going to seek criminal charges for some of his sword-swallowers. Holder is also promising to prosecute those who linked confidential wiretap information (i.e. whistleblowers).
Issa says that Holder will not prosecute any whistleblower. Holder responds that he will prosecute anyone who releases sealed wiretap information and that even the Oversight Committee may not possess that information.