'Witnesses' in the Bible

"You yourselves must be on your guard. They will deliver you up to Sanhedrins; you will be brought into synagogues and cruelly beaten; and you will stand before governors and kings for my sake, to be witnesses to them for me.

Then some came forward as witnesses and falsely declared,

At last the High Priest stood up, and advancing into the midst of them all, asked Jesus, "Have you no answer to make? What is the meaning of all this that these witnesses allege against you?"

Rending his garments the High Priest exclaimed, "What need have we of witnesses after that?