Just stating that the Judaic priesthood had forsaken the law or corrupted it remains speculation so far. Claims that the Pharisees forsook the guidance of the Torah are mostly claims based on statements of faith lacking specific verifiable evidence. The Priestly Source of the Documentary Hypothesis, the theory ascribing parts of the Old Testament to the writings of the Kohanim during their Babylonian exile (the name Pharisee is probably derived from parsi), has never been mentioned as far as I know. Kohanim are named after their eponymous ancestor: Cain. They are the sacrificial priests during the Second Temple period. Before they dwellt among the Hebrews, they were called Kenites (also derived from Cain). Moses stems from a Kenite tribe (Midians). He started worshiping the Kenite god under the guidance of his father-in-law, Jethro the Kenite priest. Moses learnt to sacrifice to the Kenite god from Jethro. (see Kenite Hypothesis)
Just stating they, these sacrificial cultists, were corrupt, led astray or didn't follow the law doesn't suffice, since many of the laws were probably written by them.
Who can then draw the line between their laws and those ordained by God himself?
Faith receives, love gives. No one will be able to receive without faith. No one will be able to give without love. Because of this, in order that we may indeed receive, we believe, and in order that we may love, we give, since if one gives without love, he has no profit from what he has given. He who has received something other than the Lord is still a Hebrew. - Gospel of Philip