Well, plus, he was afraid of another riot like the one that had taken place in the temple when he went for his visit under the banner of Caesar. The Jews got so angry that he had brought that banner into the temple that it took a legion of soldiers to put the riot down. Hundreds were killed or injured and the entire city was under heavy security. Then, at passover, there were millions of people in Jerusalem for the festival and this guy with a huge following comes to town which the Jewish leaders saw as a challenge to their authority.
I really think they were worried that Jesus was going to lead an insurrection against the temple leaders and install himself as chief priest and perhaps kill them. That's why they had him arrested on the evening of passover, because the next day was a temple day and they were thinking that when Jesus came to temple, he was going to stand up and take over, all with the approval of the people. They had to act on the passover or it would be too late. He had to be arrested, tried, convicted and executed before the first day of Unleavened Bread when everyone came to the temple.
They turned to the Roman occupation government for help. I'll bet they told the captain of the guard, "look, here's this guy Jesus, he's got a crowd of followers and he's got them all rialed up. You should have seen the scene they made last sunday when he came into town. We know he's come with his hoards to take over the city and proclaim himself king, and he's going to lead them in a rebellion and there's going to be another riot and if that happens, Rome is going to come down hard on Pilate and you. We have to arrest him tonight and get him executed before our holiday or he will raise up trouble." And the captain of the guard, worried about what would happen if Jerusalem got out of hand with millions of festival-goers in it, rushed out with Judas and the Jewish leaders to stop the rebellion before it could begin. They found him in the garden and the rest is history.
But my question is, what did Pilate know of Jesus, if anything, or was he completely clueless?