Deception comes from the Father of deception......the Devil.

The discussion in John chapter 8 goes on and gets even better. Jesus tells them bluntly that they are not the children of Abraham. (vs39-41)

 "Ye do the deeds of your father" Christ is calling them out here and later says "Ye are of your father the devil" 
so this is some very harsh thing for these guys to swallow..... and they are not doing a very good job of it. every question they ask following this just makes it worse. Christ has the pharisees pinned with something that they didn't comprehend at that moment in time. Their works were deceitful.

The Pharisees,
-said one thing and their heart was not in it.
-acted one way so the people would believe their spirituality.
-had to keep an appearance as if they were the only ones that had connection with God.
-had deceived themselves and others to believe that God honored their physical lineage from Abraham.