‘And Pilate asked him saying, “Do you answer nothing? See how many things they accuse you of.” But Jesus no longer made any reply insomuch that Pilate marvelled.''
Jesus' silence did more to convince Pilate of His innocence than any protest. He was experienced enough to recognise the special pleading of the accusers and to note that they had no real evidence. And he did not like them anyway. But neither could he understand this man who made no attempt to defend Himself. Roman justice very much depended on the defence of the accused. John also explains that he did at this stage challenge Jesus about this and that at Jesus' reply he became even more convinced of His innocence (John 19:10-11).
But John also tells us why he gave way. He gave way because he was threatened that if he let Jesus go they would accuse him to Caesar of ignoring a rebel claimant to kingship and of not being ‘Caesar's friend', a title of honour. In other words they would stir up trouble for him. He had had trouble with them in the past and so he knew that this could become serious for him. Thus just letting Jesus go would not be worth the trouble it would cause, so he therefore tried another tack. In order to understand his ‘wriggling' we have to remember that he had only recently had charges made against him to Caesar and had been reprimanded. he would not want it to happen again.
‘Pilate marvelled (thaumazein).' Consider Isaiah 52:15 LXX, ‘Thus will many nations wonder (thaumasontai) at Him, and kings will keep their mouths shut, for they to whom no report was brought concerning Him, will see, and they who have not heard, will consider'. Pilate was clearly impressed by Jesus.
But we can be sure that Jesus was well aware that the outcome of His case would not depend on the truth being established. Why waste time arguing when He knew that the case was wholly political and would be decided by political pressure? He simply refused to get involved and become embroiled with people like the Chief Priests..