Who discovers Duncan’s body in Macbeth?

In Macbeth, Macbeth and Lady Macbeth
conspire to murder Duncan so that they can satisfy their "vaulting ambition,"
(I.vii.27). Macbeth is so influenced by the prophesies of the witches who have assured
him that he "shalt be King hereafter," (I.iii.50), that he is both excited and disgusted
by his own, as he calls it, "earnest of success,"(132). Macbeth's determination wanes,
however, and it is up to Lady Macbeth to  persuade him; which she does by suggesting
that, if he does not murder Duncan and further his own aims, then he is a "coward in
thine own esteem," (I.vii.43), and is less of a man for it. Lady Macbeth goes on to
explain to Macbeth how they will kill Duncan and blame "his spongy officers," (71) for
the murder which Lady Macbeth calls "our great quell," (71). She is confident that, by
using the guards' own daggers, the guards will be found guilty. Macbeth is also
sufficiently persuaded.

Having prepared everything for
Macbeth and remarking that she would have killed Duncan herself, "had he not resembled
my father," (II.ii.12), Lady Macbeth is shocked at Macbeth's apparent confusion after
killing Duncan, especially as he has brought the daggers with him and so threatens their
plan to blame, "the sleepy grooms," (49) and she has to return them herself and hope
that their plan has not been
compromised. 

Macduff comes to
wake Duncan and after a brief exchange with Macbeth, he goes to wake Duncan. Macbeth,
trying to remain normal, chats with Lennox who remarks how the wind, during the "rough"
night, has caused chimneys to blow down and even how there were strange "lamentings,"
and even "screams of death," (II.iii.54) that made it a terrible night. When Macduff
returns to Macbeth and Lennox, he can barely contain his horror at having seen Duncan
dead and "the life of the building" (67) apparently "stole(n)." Having discovered the
body, Macduff wants to awaken the others and even tries to, ironically, protect "gentle"
Lady Macbeth from the horror.  Macbeth then tries to cover his tracks by admitting to
having killed the guards but, he claims, he did so when he saw what they had done to
Duncan. There are concerns about "treasonous malice," (131), and Macbeth will continue
scheming in an effort to ensure his place as king, at any cost.