Macbeth believes he needs to kill
What reason does Macbeth give for killing Duncan?
After receiving the prophecy from the Three Witches in Act 1, Scene 3, Macbeth immediately begins thinking about assassinating King Duncan once he learns that he has been named Thane of Cawdor. Macbeth's foremost motivation for killing Duncan is to become king of Scotland.
How did Macbeth killed the king?
King Duncan comes to stay at Macbeth's castle. Lady Macbeth tells Macbeth that she has got the King's guards drunk. ... Macbeth stabs Duncan. He comes back, covered in blood and still holding the murder weapons.