What does John 18:31 mean?

Jesus' entry into Jerusalem a few days prior (Matthew 21:1–11; John 12:12–19) was extravagant and unusual. Had there been any reason for the Roman Empire to think He was a true threat, no other evidence would have been needed for them to act. It's certain, then, that Pilate was already vaguely aware of who Jesus was, and that Jewish religious leaders hated Him (Matthew 27:18). When he asked why Jesus had been brought for judgment, the scribes and Pharisees gave a derisive answer (John 18:30).

Pilate's retort is equally snide. He's not interested in their religious bickering (Mark 15:10). Since Rome allows local religious leaders to police certain offenses, including religious ones, squabbles between rabbis should not require a governor's intervention. The mention of the death penalty, however, implies their accusations are more serious. Other passages make the strategy of Jesus' enemies clear: to paint Him as an insurrectionist (Luke 23:2) actively rebelling against Roman rule (John 19:12–15). This would allow them to not only eliminate Jesus, but to deflect any resulting anger towards the Roman occupiers, instead of themselves.