It still looks like the FBI planted false information with Seikaly at the DOJ to see if he'd leak it. When he did, the FBI had no way to prosecute someone in the DOJ without help from the DOJ, so they let the people at the DOJ handle it. Seikaly left the DOJ, and he's still sweating out possible prosecution. The FBI got what it wanted: They stopped Seikaly from leaking any more information.
Not every criminal ends up in jail. This looks like a negotiated resulution that caused the least embarrassment to all concerned.
Is it equally or more plausible that the US Attorney, head of civil, and head of criminal just left for lucrative jobs in private practice?