The leaders of Israel had already decided to do away with Jesus. His presence in Jerusalem for the Passover season gave them a chance to have Him arrested and brought to trial before Pilate and Herod Antipas. Both of these rulers were in Jerusalem for the occasion.
Luke mentioned the seven-day feast of Unleavened Bread as the better known of the two feasts whereas Matthew and Mark both featured the Passover in their accounts. Greek readers may have known this feast as the feast of Unleavened Bread more commonly than as Passover.
The Jewish religious leaders took the initiative against Jesus, but the common people did not share their antagonism. The chief priests were mainly political leaders who owed their jobs to Rome. The situation also required the legal expertise of the scribes or lawyers. The Jewish leaders could not discover a way to take Jesus without causing a riot until Judas came forward with his plan.
