A.T. Robertson Commentary Mark 11:33

"And they answered Jesus and say, We know not. And Jesus saith unto them, Neither tell I you by what authority I do these things." — Mark 11:33 (ASV)

We know not (ουκ οιδαμεν). It was for the purpose of getting out of the trap into which they had fallen by challenging the authority of Jesus. Their self-imposed ignorance, refusal to take a stand about the Baptist who was the Forerunner of Christ, absolved Jesus from a categorical reply. But he has no notion of letting them off at this point.