FBI agents who worked on the investigation of Hillary Clinton's use of a private email server reportedly had to sign an unusual non-disclosure form banning them from talking about the case unless they were called to testify.they'd never heard of the special form — known as a "case briefing acknowledgment" — being used before, though all agents initially have to sign nondisclosure agreements to obtain security clearance."This is very, very unusual. I've never signed one, never circulated one to others," one unnamed retired FBI chief tells the Post."I have never heard of such a form. Sounds strange," an anonymous FBI agent said.The Post additionally reports some FBI agents are disappointed that Director James Comey decidedagainst Clinton for her mishandling of classified information."FBI agents believe there was an inside deal put in place after the" just hours before the release of a House report on the Benghazi, Libya terror attack in 2012, one unnamed source tells the Post.Another Justice Department source tells the newspaper he was "furious" with Comey, deriding him for having "managed to piss off right and left."