Batman:

I think it would be wise to research the public record of the FBI's reliance on the polygraph in cases where informants are examined.  

A search on Google.com with the search words "FBI, polygraph, informants" will open you up to some public records that will go strongly against your suggestion that the FBI doesn't merely rely upon polygraph results.

In actuality, up until recent media attention was given to the horrendous mistakes made by the FBI's choice to follow the results of poly exams of informants (Carol Howe, OK City bombing, Emad Salam, WTC I bombing, and Abdulssuttar Sheikh, WTC II and Pentagon bombings of 9/11, just to name a few of the most serious), the FBI routinely dismissed an informant immediately upon a failure of the poly exam.  No further investigation was made into the information.  Also, any prior information provided by that particular source, valid or not, became discreditied along with the source.

You are further wrong in your claim that an informant who walks in to provide information is NOT put into the box first.  Again, a Google.com search will prove you to be wrong on that matter as well.  The FBI had a walk-in informant who gave them detailed information about the proposed events of 9/11, he or she was placed in the box, failed, and the FBI chalked it up to just being another lunatic.

Perhaps the agency that you work for does things differently.  Perhaps they value sources more than the bureau, and they try to ensure continued cooperation by not putting themselves in the position to insult a source with such nonsense as the polygraph. There are, in fact, several agencies out there who do not routinely suggest that their sources submit to polygraph examinations.  

Have you read the Statement of Agreement between the FBI and sources?  Have you read them for other agencies?  I assure you, there is quite a difference between them.

Now the bureau is facing a difficult situation publically.  They have learned that discounting information from sources based totally on the polygraph has gotten them into horrible trouble.  (Reading of Congressional Inquirys shows a lot of this, by the way.)  I just wonder when they are going to go one step further and realize what such futile faith in prescreening has done for them.  

Regardless of wether the poly is used to screen potential employees or of sources, to make a conclusion based soley on the outcome of such an inaccurate exam is totally unacceptable.

Regards,