Jesus was pronounced innocent by Pilate himself. Pilate knew that around that time "[he] should release someone to [the Judeans] at the Passover" (18:39). Thus, Pilate offered the release of Jesus, who, according to Pilate, was King of the Jews.
Although Jesus was innocent (even according to Pilate), the Judean crowd did not want Jesus freed! Especially since some of them captured Jesus and sent Him to Pilate. Rather, they wanted to free Barabbas, who was a robber (18:40). The discrepancy demonstrated that the Judean crowd was hypocritical, which reveals their attitude of not liking Jesus (likely due to pride).