Macduff goes to wake the King, but discovers he is dead. He was murdered during the night. Macbeth acts like he doesn't know what's happened with the King.
The guard was covered in blood and looked guilty, so I killed him.
Lets go together and figure out more about who committed this crime.
Macbeth and Macduff go find the King dead. Macbeth kills the guard as well, who is covered in the King's blood.
We look guilty of killing Duncan. We should leave before anyone blames us and we get in trouble.
*alarm bells are ringing* (onomatopoeia) Lady Macbeth enters and pretends she doesn't know what is happening.
Macbeth killed the guards who were supposed to be protecting the king out of "anger." He really did it so everyone would think the guards were guilty. (Macbeth, II, iii, Line 105-108) "The violent rage inspired by my love for Duncan cause me to act before I could think rationally and tell myself to pause."
I did it
After everybody leaves to discuss the crime, Malcolm and Donalbain decide to run away so they aren't accused for the murder.
Malcolm and Donalbain leave to England and Ireland, because they are suspects of killing Duncan and they don't want to get hurt. There is dramatic irony in this scene, because Macbeth was the one who killed Duncan all along, he's just pretending he doesn't know so he won't get caught.