I don’t see that the crowd that welcomed Jesus was necessarily the same crowd that condemned him. Jerulasem surely had many people who believed in Him and many who did not believe or even feared him.
We were just talking about this in Bible study this morning. I don't think they were the same crowd either as it seems like it was the crowd that came up with Jesus from Jericho who were the ones that were doing all the shouting and acclaiming as Jesus was entering the city. In fact, when they got to the city we hear that people inside were asking about Jesus, "Who is this?"
We know that that at that time, Jerusalem was swollen with pilgrims that had come to the city from all over the Roman Empire for Passover and who would probably not even heard of Jesus until this time or after he cleared the temple shortly after. I think it was people from these large crowds that more likely called for Jesus' death before Pilate.