Never mind the elaborate conspiracy theories. Brace yourselves folks, the FBI might be just as dumb and reckless as they appear to be.
point of information - William C. Patrick was not brought into the investigation by the FBI early on because he was considered a "person of interest". He was later brought in as an expert after he passed a polygraph. One indication at least that the FBI took seriously its domestic terrorist theory.
The Barbara Hatch Rosenberg Cabal still consider him a person of interest.