they not only mocked Jesus, but the jewish religous leaders who set up Jesus for death.

When you think about this kind of cruelty that Jesus suffered for our transgressions and the roman soldiers dishing this out one can only come to one conclusion and that is they had sordid spirits, evil hearts controled by satin. All this was foretold in Isiah, which means God was and is in control of all that took place for our benefit. 

Many of the elders and those who supported the elders wanted to see JESUS crucified, because they were afraid of JESUS, his radical teachings (radical from their perspective) and ability to amass large followings. Despite all of this, they were willing to gamble and release Barabbas and take their chances that his release was less of a risk then keeping JESUS alive.