The turning of the crowd.

In the Bible, we see huge crowds flocking to Jesus. We hear of him feeding the 10,000, the 5,000 - we read the accounts of the packed house, the full bay. How, then, did this all change so suddenly - how did these people who followed Jesus and loved him so much yell "Crucify him!"? Was it God turning their hearts, so that his plan could go ahead? Or were their hearts turned already? Let's have a look.
Shortly before Jesus was arrested, we have him riding into Jerusalem on a donkey. Palm Sunday - most people probably know the story, but do you know it all? The people were shouting "Hosanna" - that means, "save us". They were crying to Jesus to save them. But not from their sins, as he came to do. From the Romans, as the conquering, warrior-King Messiah.
And then Jesus gets arrested. By the Romans. And he doesn't even fight back. In fact, when one of his disciples does fight back and chop a soldier's ear off, he heals it back.
This man, who the Jews thought was going to conquer the Romans, save them from their rule - had just been arrested by them, healed one of them, and was set for execution. It's like all that the Jews thought he had promised them, he was breaking. He didn't care. He wouldn't save them.
And so they turned. The crowd turned. And Jesus was crucified. And they were saved. But from their sins, not the Romans.