what does Banquo think about Macbeth at this point in the play

Alone at Macbeth's court, Banquo voices his suspicions that Macbeth has killed Duncan in order to fulfill the witches' prophesies.

"Thou hast it now: King, Cawdor, Glamis, all, As the Weird Women promis'd; and I fear, Thou play'dst most foully for't..." Act 3 sc1

He muses that perhaps the witches' vision for his own future will also be realized, but pushes the thought from his mind.