Mark 15: 1-20, Pilate's verdict

The Jewish leaders want Jesus killed for "blasphemy".  But now they need the help of the Romans.

Mark 15: 1-5
Very early in the morning, the chief priests, with the elders, the teachers of the law and the whole Sanhedrin, reached a decision. They bound Jesus, led him away and handed him over to Pilate.

"Are you the king of the Jews?" asked Pilate. 

"Yes, it is as you say," Jesus replied.

The chief priests accused him of many things. So again Pilate asked him, "Aren't you going to answer? See how many things they are accusing you of."

But Jesus still made no reply, and Pilate was amazed.

Jesus is quiet and confident before Pilate, not the typical behavior of a man about to be executed.  The Jewish charge of blasphemy is not particularly important to Pilate and so he is attempting to get more information and find a greater crime.

Mark 15: 6-14
Now it was the custom at the Feast to release a prisoner whom the people requested. A man called Barabbas was in prison with the insurrectionists who had committed murder in the uprising.

The crowd came up and asked Pilate to do for them what he usually did. "Do you want me to release to you the king of the Jews?" asked Pilate, knowing it was out of envy that the chief priests had handed Jesus over to him.

But the chief priests stirred up the crowd to have Pilate release Barabbas instead.

"What shall I do, then, with the one you call the king of the Jews?" Pilate asked them.

"Crucify him!" they shouted.

"Why? What crime has he committed?" asked Pilate. 

But they shouted all the louder, "Crucify him!"

Pilate believes that the crowd is not particularly sympathetic with the self-righteous religious leaders and expects Jesus's popularity with the common people will play out here.  He sees a route out of his dilemma: let the crowd ask for the release of Jesus.

But the religious leaders have outplayed him; they have "stirred up" the crowd, possibly bringing their own supporters, very likely drumming up the charge of blasphemy. Once Pilate has offered the crowd a choice, he has implicitly agreed to condemn one of the two men, Jesus or Barabbus, and so he is trapped.

Mark 15: 15-20
Wanting to satisfy the crowd, Pilate released Barabbas to them. He had Jesus flogged, and handed him over to be crucified. The soldiers led Jesus away into the palace (that is, the Praetorium) and called together the whole company of soldiers. They put a purple robe on him, then twisted together a crown of thorns and set it on him. And they began to call out to him, "Hail, king of the Jews!"

Again and again they struck him on the head with a staff and spit on him. Falling on their knees, they paid homage to him.  And when they had mocked him, they took off the purple robe and put his own clothes on him. Then they led him out to crucify him.

Releasing the prisoner to the soldiers for crucifixion gave implicit permission for the soldiers to play with their victim.  They take advantage of it.