FBI Confirms 'Gag Order' On Agents Investigating Clinton

The FBI has confirmed to a senior Republican senator that agents were sworn to secrecy -- and subject to lie detector tests -- in the Hillary Clinton email probe, an extensive measure one former agent said could have a "chilling effect."

A July 1 letter sent by a senior deputy to FBI Director James Comey to Senate Judiciary Committee Chairman Charles Grassley, R-Iowa, detailed the restrictions on agents. The letter, reviewed by Fox News, confirmed agents signed a "Case Briefing Acknowledgement" which says the disclosure of information is "strictly prohibited" without prior approval, and those who sign are subject to lie detector tests.

The measures show the extent to which the bureau has gone to keep additional details of the politically sensitive case from going public.

A recently retired FBI agent, who declined to speak on the record, citing the sensitivity of the matter, said a "Case Briefing Acknowledgement" is reserved for "the most sensitive of sensitive cases," and can have a "chilling effect" on agents, who understand "it comes from the very top and that there has to be a tight lid on the case."

Comey said last week more than 100 classified emails were sent or received by Hillary Clinton, including some at the Top Secret level, which would require agents to have the necessary clearance to review and investigate.  Some of the intelligence came from the U.S. government's most closely held programs, known as Special Access Programs, or SAP and included human spying.

The "Case Briefing Acknowledgement" is more evidence that the probe was always a serious criminal investigation, and never a "security review" or "security inquiry" as described by Clinton and her campaign team.

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