Whom do Macbeth and Lady Macbeth plan to blame for Duncan's murder?
In Act 1, scene 7, it is Lady Macbeth who recommends that the blame for Duncan's murder should be pinned on his two chamberlains who will be in his bedchamber with him in order to protect him as he sleeps. She does this because her husband has expressed doubt that their malicious venture will succeed. He is obviously concerned that they will become the prime suspects and Lady Macbeth's plan evidently comforts him. She tells Macbeth:
...What cannot you and I perform upon
The unguarded Duncan? what not put upon
His spongy officers, who shall bear the guilt
Of our great quell?
She refers to Duncan's two guards as 'spongy' for they would have soaked up all the wine and all sorts of alcoholic beverages that she would have plied them with. They would be in a stupor and would, therefore, be unable to perform the task of protecting their liege. Furthermore, they would be so inebriated that they would, as a consequence, obviously be fast asleep during the assassination and she and her husband would be able to easily plant evidence on them to implicate them.
Macbeth is impressed with his wife's plan and comments on her daring, stating that she should bear male children only, for they would supposedly be born with that same quality. He then further suggests, by asking a rhetorical question, that they should smear the sleeping guards with Duncan's blood and use their daggers to commit their foul act. Suspicion would then immediately fall upon the guards since the circumstantial evidence would point out their guilt.
Lady Macbeth comments that no one would dare think differently, for she and her husband would loudly express their grief and create a huge uproar about the king's untimely and callous death. Macbeth then expresses his satisfaction with the plan and wholly commits himself to the commission of their pernicious deed.
One must agree that the plan seems sound on the surface, but there are many loose ends. The guards would, firstly, definitely be questioned and deny any wrongdoing. Secondly, they might implicate Lady Macbeth by mentioning how she urged them to drink and provided them with copious quantities of alcohol. Thirdly, they would lack motive. Furthermore, if they were so drunk, how would they even have had the ability to commit the deed? And, lastly, it would not make sense that they would, after committing such a terrible and treasonable act, go back to sleep.
Macbeth must have realized later, in Act 2, scene 3, after the assassination, that their plan would not completely work and so, to avoid any doubt, he decides to murder the guards in their sleep as well. When Macduff questions his motive for doing so, he mentions that he acted out of impulsive passion borne from his love and loyalty to his king. He states that after he had seen the murderers covered in Duncan's blood:
...who could refrain,
That had a heart to love, and in that heart
Courage to make 's love known?
Macduff, however, is not entirely convinced, and later refuses to attend Macbeth's coronation at Scone. He wishes Ross well on his journey there and cryptically states that he hopes his comrade sees that things are done well at Scone since he fears that their old robes might sit easier than their new. The implication is clear: Life under Macbeth's rule might be more uncomfortable than when Duncan was king.
Lady Macbeth comes up with the idea to frame Duncan's own "chamberlains" (servants of his bedchamber) for his murder. In Act 1, Scene 7, she says,
When Duncan is asleep [...],
his two chamberlains
Will I with wine and wassail so convince
That memory, the warder of the brain,
Shall be a fume, and the receipt of reason
A limbeck only. When in swinish sleep
Their drenched natures lies as in a death,
What cannot you and I perform upon
Th' unguarded Duncan? (lines 71-80)
In other words, she will get them very drunk, so drunk that they lose all ability to reason, and they will not be able to remember anything the next day. She claims that, with them sleeping off all this alcohol, she and Macbeth can do whatever they want to Duncan because they won't have the sense or ability to stop them.
Later, in Act 2, Scene 2, after Macbeth has committed the murder, he brings the daggers he used from the room. Lady Macbeth chastises him for his failure to reason, saying
Why did you bring these daggers from the place?
They must lie there. Go, carry them and smear
The sleepy grooms with blood. (lines 62-64)
When Macbeth refuses, she does it herself. Finally, in Act 2, Scene 3, after Macduff discovers Duncan's body the next morning, Macbeth and Lennox go into the bedroom to see for themselves. While there, Macbeth kills the two chamberlains, claiming that
Th' expedition of [his] violent love [for Duncan]
Outrun the pauser, reason [....].
Who could refrain
That had a heart to love, and in that heart
Courage to make 's love known? (lines 129-137)
He claims that he loved Duncan so much that his anger at Duncan's murderers got the best of him. He then implies that anyone who would do less does not love Duncan as much as he does. It is no small coincidence that this also removes those chamberlains' ability to say who got them drunk and anything else they might remember from the night before.
Since the murder of Duncan was committed offstage, Shakespeare apparently wanted to show as much blood as possible in order to create a strong impression on his audience that a terrible murder has been committed. This seems to explain why Macbeth returns to his bedchamber with two bloody daggers which his wife tells him he should have left by the grooms after smearing them with the dead King's blood. Macbeth is too unnerved by what he has already done to follow his wife's orders. He says:
I'll go no more.
I am afraid to think what I have done;
Look on't again I dare not.
This is one of Shakespeare's many ways of ameliorating Macbeth's guilt in killing the King, since the playwright wanted to retain some modicum of audience sympathy for Macbeth in what is Macbeth's tragedy. In doing this, Shakespeare passes more of the guilt along to Lady Macbeth. She is forced to take the daggers back to the King's chamber and do what her husband could not. When she returns, she now has bloody hands too. This doubles the quantity of blood that Shakespeare displays to his audience. No doubt when she says
My hands are of your color, but I shame
To wear a heart so white
she wipes her bloody hands across her white nightgown in the area of her heart. So the bloody couple represent the bloody murder of King Duncan which Shakespeare decided not to show but to let his audience imagine. The playwright probably decided not to show Duncan being murdered because it would be too hard to stage and might not be visually effective. Shakespeare may have also had Macbeth commit the murder offstage in order to minimize his guilt. Duncan's bloody body is never seen but only described. When Macduff discovers the body, he does so offstage. And when Macbeth murders the two innocent grooms, this is also done offstage.
The MacBeths plan to set up the drunken servants by covering them with Duncan's blood and leaving the bloody daggers with them so that when the scene is discovered, they are visually implicated. Unfortunately, MacBeth is so overcome by his murderous act that he forgets to leave the daggers with the servants and Lady MacBeth has to "plant" the daggers. To further compound the botched coup, when MacDuff "discovers" the carnage, MacBeth in a rage bursts into the room and slays the drunken servants. This seems too rash, too "convenient" to both MacDuff and Banquo. They suspect MacBeth has committed regicide.