Complex sentence: He may at first have been a sincere believer in the existence of the plot along with much of the general populice and parliament, regardless he did nothing to test the credibility of witnesses as Oates, Bedloe and Dangerfield.
Split into simpler sentences: He may at first have been a sincere believer in the existence of the plot along with much of the general populice and parliament. Whether he believe the plot was real or not he did nothing to test the credibility of witnesses as Oates, Bedloe and Dangerfield.