Question: At the time of Jesus' trial, who was in prison for being a notorious poltical agitator?
Answer: Barrabas was chosen by the crowd, over Jesus, to be released by Pontius Pilate in a customary pardon before the feast of Passover.
Bonus Question: How many times did Paul deny Jesus?
Bonus Answer: It was Peter who denied Jesus, not Paul. (I didn't read the question carefully either!) Paul was actually not one of Jesus' original disciples but converted after Jesus' resurrection and ascension.