Answer:
When Macbeth poisoned? King Duncan he framed the king's guards. When the sons found out their dad was dead and thought the guards did it, they fled before the guards can blame them because they thought that was going to happen. And usually when someone flees a scene very quickly after finding bad news they're racked up with guilt so if they were to come back they would be incriminated for their father's death.
hope this helps, i haven't read the book in about two years.
