I know that they stoned Stephen, but they took Jesus to Pilate because they did not have the authority to put someone to death.
John 18:28-31 - Then led they Jesus from Caiaphas unto the hall of judgment: and it was early, and they themselves went not into the judgment hall lest they should be defiled; but that they might eat the passover. Pilate then went out unto them and said, What accusation bring ye against this man? They answered and said until him, If he were no a malefactor, we would not have delivered him up unto the. Then said Pilate unto them, Take ye and judge him according to your law. The Jews therefore said unto him, It is not lawful for us to put any man to death.
Wrong! You might note that this was news to Pilate.
This was Jewish law not Roman and it had to do with the Passover. If they had chosen any other time then they could. That is why they took him to Pilate. Not because they couldn't at any time but because of the time of the year it was they would have defiled themselves.
This was a passing of the buck. They wanted Jesus gone and, maybe deliberately, they chose the one time of the year when they, by their law not Roman law, would have to have the Romans do it.