The Son of the Father
Pilate brings up the tradition of releasing a prisoner as a sign of goodwill. The guy's name was Barabbas. Interestingly enough, the man's name means "Son of the Father" so Pilate is asking to release this "son of the father" or that "Son of the Father" (since Jesus is God's Son).
Matthew 27:17New American Standard Bible: 1995 Update
So when the people gathered together, Pilate said to them, “Whom do you want me to release for you? Barabbas, or Jesus who is called Christ?”