Who is responsible for the murder of Duncan?Is it Macbeth , Lady macbeth or the witches?I have the witches prophecies, Lady Macbeth's contribution...

In the first scene of Macbeth by
William Shakespeare, the newly made Thane of Cawdor hears the prophecy of the three
sisters and thinks,

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If chance wil have me King, why, chance may
crown me,

Without my stir.
(1.3.145

But, later he
ponders what is to come.  Then, when Duncan arrives at Forres and compliments Macbeth,
the King declares his son Malcolm as his successor, naming him Prince of Cumberland. 
This act puts an obstacle in the path of Macbeth who now desires to be
king:

The
Prince of Cumberland!  That is a step

On which I must fall
down, or else o'erleap,

For in my way it lies.  Stars, hide
your fires;

Let not light see my black and deep
desires:

The eye wink at the hand; yet let that
be

Which the eye fears, when it is done, to see.
(1.4.55-60)

From this
passage, it is implicit that Macbeth has taken the predictions of the witches and suited
them to his own "vaulting ambition" which he himself says "o'erleaps" in his soliloquy
of Scene 7, thus tying his thoughts to those expressed in Scene 4.  After returning to
his castle where Duncan is due to arrive, he shows some reluctance about slaying
Duncan.  But, his wife, Lady Macbeth scolds him, telling him
to

...screw
your courage to the sticking-place

And we'll not fail (1.7.
68-69)

Interestingly, there
are three witches, and three accomplices in the murder of Duncan:  the supernatural,
Macbeth himself and Lady Macbeth, two triangles of
evil.