Macbeth admits the murders to his wife and hired murderers, who are already privy to the crimes, as well as to the audience. In his soliloquy at the beginning of Act III, he says of Banquo's issue, "For them have I the royal Duncan murdered." That's an admission but only the audience hears it. In a way, he also admits the slaughter of Macduff's family when he says to him in Act V, "my soul is too much charged with blood of thine already."
The king
Duncan's grooms, who he and Lady Macbeth have framed for the murder of Duncan. He claims to have been infuriated at their apparent guilt, when in fact he just wanted to shut them up.
And then Macbeth asked Macbeth if he confronted Macbeth on killing Macbeth with Macbeth.
Macbeth's coronation
Macbeth believes he has to kill Duncan's guards in case they heard anything happen in the room while Macbeth was killing Duncan.
The king
Duncan's grooms, who he and Lady Macbeth have framed for the murder of Duncan. He claims to have been infuriated at their apparent guilt, when in fact he just wanted to shut them up.
Lady Macbeth talked Macbeth into killing his cousin, King Duncan of Scotland, who was a guest in his house at the time.
And then Macbeth asked Macbeth if he confronted Macbeth on killing Macbeth with Macbeth.
She helps Macbeth out by tricking him into killing the king. :P
Macbeth's coronation
Macbeth kills Banquo in the play and then Banquo's ghost haunts Macbeth.
Macbeth believes he has to kill Duncan's guards in case they heard anything happen in the room while Macbeth was killing Duncan.
she talked him into killing the King by accusing Macbeth of being weak and cowardly
Because you don't mess with Lady MacBeth
"Sleep no more, Macbeth doth murder sleep."
Macbeth kills Duncan's grooms after Macduff discovers the body.