They feared (ephobēthēsan). This is the explanation. They became frightened for their own lives when they saw what they had done to Roman citizens.
They asked (ērōtōn). Imperfect active of erōtaō. They kept on begging them to leave for fear of further trouble. The colonists in Philippi would turn against the praetors if they learned the facts, proud as they were of being citizens. This verb in the Koiné is often used as here to make a request and not just to ask a question.