What does Acts 25:4 mean?

Porcius Festus is the new governor of the districts along the shore of the eastern Mediterranean Sea. He'd only been in his capital, Caesarea Maritima, three days before he traveled to meet with the Jewish leaders in Jerusalem.

Festus had replaced Felix. This happened after the people of Caesarea complained so much that the Emperor—the infamously tyrannical Nero—called Felix to Rome to answer for his cruelty and corruption. Festus wishes to make a good impression with the locals, and he does so. History reports that he was fair and reasonable. He even eliminated the Sicarii: the assassins Felix sometimes used to keep the peace. He's not very well-versed in the culture (Acts 26:24), however, and although he knows about Paul, he may not know the whole back-story.

Two years prior, Paul had been the victim of a smear campaign. Individuals and groups accused him of things like rejecting the Mosaic law and desecrating the temple (Acts 21:20–21, 27–28). When the Roman army tribune brought him before the Sanhedrin to get clarity on the matter, Paul insulted the high priest and managed to goad the members into a fight (Acts 23:6–10).

The Sanhedrin responded initially by trying to use the tribune to enable a plot to assassinate Paul (Acts 23:12–15). When Paul's nephew foiled their plans (Acts 23:16–22) and the tribune sent Paul to the governor (Acts 23:23–24), the Sanhedrin brought formal charges against Paul. Since they had no evidence or witnesses, Felix refused to convict him but kept him under house arrest (Acts 24).

As soon as the Sanhedrin meets the new governor, they ask for a formal favor: to bring Paul to Jerusalem for a new trial (Acts 25:2–3). Festus knows Paul is in Caesarea, but it's unclear how much else he understands. He invites the Sanhedrin to send representatives for a hearing to determine if they have a case…which they do not (Acts 25:18–20).