Note: I believe that the following question is a question of hermeneutics, because exegesis is defined as "a critical interpretation or explanation of the Bible".
I would post the relevant passages, but they are too long to post. They are Matthew 27:15-26, Mark 15:6-15, Luke 23:15-25, and John 18:39-40.
I heard Richard Carrier argue that the story of Barabbas is fabricated and based on the ritual in the Mosaic Law where one lamb was killed as a sacrifice and another was let into the wilderness, found in Leviticus 16.
He says that the name Barabbas is an extremely unusual name, and means "son of a father", which corresponds to what Jesus Christ was, the Son of God the Father. Jesus and Barabbas, therefore, were both "lambs" of the same sort. Added to this is the fact that Barabbas was an insurrectionist, and Jesus was accused of potentially instigating an insurrection, which was ostensibly why He was crucified.
He also says that there is no record of the custom of releasing a prisoner at the Passover outside of the Gospels, and so it was most likely fabricated, adding credence to the idea that the story was invented.
Carrier says that Barabbas was the lamb that was freed set free, and that Jesus was the lamb that was killed as a sacrifice.
Is this theory substantiated?