In Act 2, Macbeth, urged on by his wife, murders Duncan. He feels great remorse for this act, even to the point of near-madness, as he hears voices in his head accusing him of the murder. By Act 3, however, he has become convinced that Banquo and his son Fleance represent a threat to him, and must be eliminated. He hires two assassins to commit the deed, but Fleance escapes. There are two remarkable differences between his behavior in Act 2 and in Act 3, however. First, he does not consult with his wife about the murders, a sign that his ambition has carried him beyond even what she was willing to do. Second, he initially shows no remorse for the death of Banquo. But as the act moves along, he begins to be tormented by paranoia that he will be discovered, especially after the dramatic scene where he is visited at a banquet by Banquo's ghost:
It will have blood, they say. Blood will have blood. Stones have been known to move, and trees to speak. Augurs and understood relations have by magot pies and choughs and rooks brought forth the secret'st man of blood.
While it might be a stretch to call him genuinely remorseful for his actions, he fears that they will come back to haunt him. He is near madness, and is both drunk with power and ambition, and simultaneously full of fear that both will destroy him.