How was Don John's evil plot stopped? Who saved the day and how?

Dogberry has brought Borachio and Conrad before the town Sexton and is trying to make them confess. They refuse to cooperate. The Sexton then makes the watchman who overheard them describe what they said. He reveals the plot against Hero and the Sexton tells them that Don John secretly left that morning after Hero fainted and died. The men are ordered bound and taken to Leonato's.