A Few Cases...

from Shakespeare's Macbeth, Act 5, Scene 1:

Enter a Doctor of Physic and a
Waiting-Gentlewoman

DOCTOR: I have two nights watched with you, but can
perceive no truth in your report. When was it she last walked?

GENTLEWOMAN: Since his majesty went into the field, I have
seen her rise from her bed, throw her night-gown upon her, unlock her closet,
take forth paper, fold it, write upon't, read it, afterwards seal it, and again
return to bed; yet all this while in a most fast sleep.

DOCTOR: A great perturbation in nature, to receive at once the
benefit of sleep, and do the effects of watching! In this slumbery agitation,
besides her walking and other actual performances, what, at any time, have you
heard her say?

GENTLEWOMAN:  That, sir, which I will not report after her.
DOCTOR:  You may to be:  and 'tis most meet you should.
GENTLEWOMAN:  Neither to you nor any one; having no witness to confirm my
speech.
Enter LADY MACBETH, with a taper
Lo, you, here she comes!  This is her very guise; and, upon my life, fast
asleep.  Observe her; stand close.
DOCTOR:  How came she by that light?
GENTLEWOMAN:  Why, it stood by her; she has light by her continually; 'tis
her comand.
DOCTOR:  You see, her eyes are open.
GENTLEWOMAN:  Ay, but their sense is shut.
.....................................................................................The answer to the question in the title is: "possibly." While I have never
been involved in any legal case where sleepwalking was an issue, the situation
is interesting enough to recount a few cases and discuss the problem.
The
first recorded case apparently dates to 1846. According to the BBC (as
quoted in Wikipedia), there are now 68 known cases of "homicidal
somnambulism." When they come to court the defense against murder charge has
been on the order of: "I was sleepwalking and therefore, ladies and gentleman of
the jury, I was not myself at the time I murdered [her/him]...and so deserve
acquittal."
On a more legal basis, the argument has been:
'The defendant was not in
his normal state of mind when he committed the act. Sleep walking is a parasomnia manifested by
automatism; as such, harmful actions committed while in this state
cannot be blamed on the perpetrator.'
The argument has been successful at times. Two of three well know trials for
murder while sleep walking ended in acquittal, the other in a conviction for
murder. Coincidentally, two of the trials (one conviction, one acquittal)
occurred in the Phoenix area, and were tried in the same legal jurisdiction
(Maricopa County Superior Court). I will present those three cases,  plus a
non-murder sleepwalking defense case from Australia.