Describe Macbeth as the murderer.
We first hear of Macbeth as a murdering hero. The Bleeding Captain says he unseems the traitor Macdonwald from his belly button to his throat, but since it is on the battlefield, it is not technically murder.
Later, Macbeth will murder the king. Regicide is the most heinous crime a Thane can commit. As the King was thought to have answered to no one but God, regicide is the equivalent of murdering God.
After Macbeth murders Duncan, horses eat each other and owls eat ravens. Even the animal kingdom is affected by the murder, which is to say that the natural order has been subverted. When a murderer of a king will become king, then good becomes evil, the strong become weak, "fair" becomes "foul." Murder turns the natural order into chaos and morality into immorality.
Macbeth also murders "sleep." Macbeth thinks he hears someone say, "Sleep no more. Macbeth hath murdered sleep." This is a kind of supernatural prophecy, for the Macbeths will not be able to rest easy for the rest of the play--such is their immediate guilt. Macbeth also murders time, in that his days and nights will run together, toward death and madness. Time is measured by the sun, and after the murder the sun stops shining on the Macbeths.
Macbeth says that to be king is nothing. He wants to be safely king. He worries about Banquo, because the witches have promised that he will sire a line of kings. Macbeth, therefore, kills his best friend and would have killed his son, had he not escaped. Even children are not safe.
Macbeth, as a murderer, will say that he's swimming in so much blood that it will be easier to keep swimming (murdering) than to stop. So "blood will have blood." The murdering will continue.
After he hears the Witches say "Beware Macduff," Macbeth tries to murder Macduff. Macduff has fled, but Macbeth still murders his entire castle, wife and young son included. They were no immediate or future threat to him, like Banquo's son. But, he kills them anyway, to be safe.
Macbeth feels invincible as a murderer, especially after the Witches say he has none of woman born to fear. He kills Young Siward with the coldness of a seasoned murderer. It is only after Macduff says, "I was from my mother untimely ripped" that Macbeth begins to feel mortal. He loses his head, and the play ends the same way it began: with a murderous battle.