The FBI's pre-employment polygraph guidelines, taken from the FBI Manual of Investigative Operations and Guidelines, are now available on AntiPolygraph.org at:
http://antipolygraph.org/documents/fbi-polygraph-guidelines.shtml
Note that these guidelines clearly state, at para. 67-7.10 (4):
Quote
A preemployment polygraph examination is one element of the overall applicant screening process. It is not to be considered as a substitute for a thorough and complete background investigation....
Yet for those who "fail" or whose charts are scored as "inconclusive," the polygraph
is "a substitute for a thorough and complete background investigation." Their applications are, in nearly all cases, summarily terminated. No further investigation is conducted.