In Act 1, scene 5, when Lady Macbeth receives the letter from her husband, she vows that her husband will become king and she asks the "...spirits that tend on mortal thoughts..." to "...fill [her] from the crown to the toe, top-full / Of direst cruelty!" It is clear that she is going to do whatever she can to convince her husband to do whatever it takes to become king, including to kill the current king. When Macbeth tells his wife in Act 1, sc. 7, that he's decided not to kill Duncan, Lady Macbeth verbally assaults him. She tells him that he isn't a man in her eyes if he does not carry out the murder of the king. She hits him where she knows it will hurt the most - in his masculinity. She outlines the plan for him; she is definitely in control in Act 1. In Act 2, right after the murder, she tells her husband to be strong and to remember that there is a prize at the end of this bloody work - the crown. Again, she seems to be the one doing the driving. Even as late as Act 3, sc. 4, when Macbeth sees Banquo's ghost at the banquet, Lady Macbeth, after sending home all the guests and making an excuse for her husband's behavior, chastises her husband for letting his emotions and worries get the better of him.
Because she is the one who decided that Duncan must die so Macbeth could become king, she convinced her husband to do the deed, and she even planned it, she bears a great deal of responsibility for the bloodshed. Certainly Macbeth bears some of it, too, because he is the one who actually killed Duncan and ordered many of the deaths that followed, but if Lady Macbeth hadn't started the process with her steely determination to see her husband as king, none of the rest of the deaths would have occurred.
although lady macbeth may not have murdered king duncan herself, she is the one who led macbeth murder king duncan. i believe that without lady macbeths opinion and pushing towards the death of king duncan, it would not have been done the way it was. i also believe the story would have been totally different. to me, lady macbeth is the true murderer in "Macbeth" So, i must agree with what luannw has said.