Luke 23:6-7

‘But when Pilate heard it, he asked whether the man were a Galilean. And when he knew that he was of Herod's jurisdiction, he sent him to Herod, who himself also was at Jerusalem in these days.'

At the mention of Galilee Pilate pricked up his ears. If the man was a Galilean then perhaps Herod would know what He was talking about. For he himself certainly did not. (Compare how Festus consulted with Agrippa - Acts 25). So he sent him to Herod, who was also in Jerusalem for the Passover, not so that Herod could try Him, but in order that he might investigate the matter and give his views on the matter.