The "trials" they held were kangaroo courts in every sense and his conviction was no more than a wink-and-a-nod between buddies. When they presented Jesus to Pilot, they knew Pilot would go along with the program. He had political problems of his own. Even if Pilot knew that Jesus' conviction didn't measure up to the remedy required by law, he wasn't going to make trouble with the Jews, the ultimate special interest group of their day.
Worst of all, when given the chance repeatedly by Pilot to pick a criminal who would receive a reprieve, they didn't pick Jesus (though when read in certain tones, Pilot's words sound like an appeal to the Jews to let Jesus go).
Jesus was least successful in convincing those he came specifically to save. A select group of Jews followed him, as did many gentiles, and eventually, the remnants of the Roman Empire. The Romans were the executioners as Jesus was actually killed by their hands--but the Jews were the ones who condemned him to death, without the appearance of blood on their own hands.