Consent (suneudokeite). Double compound (sun, eu, dokew), to think well along with others, to give full approval. A late verb, several times in the N.T., in Acts 8:1 of Saul's consenting to and agreeing to Stephen's death. It is a somewhat subtle, but just, argument made here. Outwardly the lawyers build tombs for the prophets whom their fathers (forefathers) killed as if they disapproved what their fathers did. But in reality they neglect and oppose what the prophets teach just as their fathers did. So they are "witnesses" (marture) against themselves ( Matthew 23:31 ).