William Barclay (Daily Study Bible on Mark 15:5) writes:-
There is a time when silence is more eloquent than words, for silence can say things that words can never say.
(i) There is the silence of wondering admiration. It is a compliment for any performance or oration to be greeted with thunderous applause, but it is a still greater compliment for it to be greeted with a hushed silence which knows that applause would be out of place. It is a compliment to be praised or thanked in words, but it is a still greater compliment to receive a look of the eyes which plainly says there are no words to be found.
(ii) There is the silence of contempt. It is possible to greet someone’s statements or arguments or excuses with a silence which shows they are not worth answering. Instead of answering someone’s protestations the listener may turn on his heel and contemptuously leave them be.
(iii) There is the silence of fear. An individual may remain silent for no other reason than that he is afraid to speak. The cowardice of his soul may stop him saying the things he knows he ought to say. Fear may gag him into a shameful silence.
(iv) There is the silence of the heart that is hurt. When a person has been really wounded he does not break into protests and recriminations and angry words. The deepest sorrow is a dumb sorrow, which is past anger and past rebuke and past anything that speech can say, and which can only silently look its grief.
(v) There is the silence of tragedy, and that is silent because there is nothing to be said. That was why Jesus was silent. He knew there could be no bridge between himself and the Jewish leaders. He knew that there was nothing in Pilate to which he could ultimately appeal. He knew that the lines of communication were broken. The hatred of the Jews was an iron curtain which no words could penetrate. The cowardice of Pilate in face of the mob was a barrier no words could pierce. It is a terrible thing when a man’s heart is such that even Jesus knows it is hopeless to speak. God save us from that!’ (DSB)
(Wording slightly altered – Barclay was too much in the habit of referring to a Christian as ‘a man’! I’m not persuaded that Jesus silence before Pilate is ‘the silence of tragedy’, but I’ll let that pass for the moment)