Who is the Third Murderer?

Who is the Third Murderer? The play never names this mysterious character that claims to have been sent by Macbeth. There are many possibilities on the identity of the Third Murderer. Some may say it was Lady Macbeth. However, Macbeth makes sure in the scene before that she knows nothing about his plan to murder Banquo. He tells her to ?be innocent of the knowledge, dearest chuck, / till though applaud the deed.? Macbeth is sure that his wife knows nothing about the murder that he has planned for Banquo and his son, until after it is finished. He is sure to keep his wife in the dark. Therefore to my reasoning, the Third Murderer could not be Lady Macbeth.
Some say it might have been Macbeth himself who carried out the deed. Being as paranoid as he is at this time, it would rest his mind if he made sure Banquo and Fleance were dead with his own two eyes. However, the other two murderers would have instantly recognized Macbeth had he appeared beside them. Macbeth also would have to be the host at his banquet, and could not be at two places at once. When he saw one of the murderers at his banquet door, he was anxious to know what happened. If he had committed the murder, he wouldn?t have been so nervous. So I also believe Macbeth was not the Third Murderer.
Now comes Lennox. He?s a nobleman of Scotland. A warrior, if it can be said. He hungers for power, or at least association with power. At the banquet, he is the first to offer Macbeth a seat next to him. Perhaps to talk about a murder he just committed? When the guests leave, Lennox is the last to go. He bids the king good health, probably to be more highly favoured. However, I do not believe that Lennox was the murderer. Surely Macbeth would have seen right through him. Lennox quickly switches sides with Macbeth when he learns the Malcolm is about to wage war. For if Macbeth loses, how will he, Lennox, be looked upon? This kind of frail loyalty would not have pushed Lennox to do such a wicked thing as murder.
And then there is Ross, the harbinger of news, whether it be good or bad. He informed Duncan about the victory of Macbeth over Sweno (perhaps hinting at his reverence for Macbeth at an early stage). While talking to Macduff in Act 2, Scene 4, he guesses that the crowning will be passed to Macbeth. He also realizes that Macduff is an enemy of Macbeth, for he tells Ross that he refuses to see him crowned at Scone. Ross could have been the third murderer; Macbeth would have trusted someone who was loyal to him even before Duncan was killed. Since it was not the Third Murderer who actually performed the murder (that was the First Murderer), his clothes would not have been stained with blood at the banquet. While Banquo dies, he shouts an interesting line: ?Though mayst revenge. O slave!? Ross is a nobleman, and a servant therefore to his king, Macbeth. Is Banquo saying by this line that Ross admires Macbeth so much that he is prepared to do anything to please him? A few lines before that, the first Murderer states, ?his horses go about.? The Third Murderer replies ?Almost a mile; but he does usually--/ So all men do?from hence to the palace gate/ Make it their walk.? That shows he has a fairly good understanding of how the castle operates. He knows the custom that people take while entering the castle, showing that he would have seen this often.
I believe that Ross is the Third Murderer. Later in the play, he, in effect, kills his own cousin and nephew. If one can carry out such a thing as this and live with the guilt, what doubt is there that Ross could murder a human being with no blood relation? He carries the news to Macduff that his wife and children are dead, perhaps to sorrow him and make him unfit for battle with Macbeth