'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.

Now the chief priests and the whole council sought witnesses against Jesus to put him to death, and found none.

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?"

Then the high priest rent his clothes, and saith, What need we any further witnesses?