(a) Before the jury retires for deliberation, the judge must give an instruction which informs the jury that in order to return a verdict, all 12 jurors must agree to a verdict of guilty or not guilty.
(b) Before the jury retires for deliberation, the judge may give an instruction which informs the jury that:
(1) Jurors have a duty to consult with one another and to deliberate with a view to reaching an agreement, if it can be done without violence to individual judgment;
(2) Each juror must decide the case for himself, but only after an impartial consideration of the evidence with his fellow jurors;
(3) In the course of deliberations, a juror should not hesitate to reexamine his own views and change his opinion if convinced it is erroneous; and
(4) No juror should surrender his honest conviction as to the weight or effect of the evidence solely because of the opinion of his fellow jurors, or for the mere purpose of returning a verdict.
(c) If it appears to the judge that the jury has been unable to agree, the judge may require the jury to continue its deliberations and may give or repeat the instructions provided in subsections (a) and (b). The judge may not require or threaten to require the jury to deliberate for an unreasonable length of time or for unreasonable intervals.
(d) If it appears that there is no reasonable possibility of agreement, the judge may declare a mistrial and discharge the jury. (1977, c. 711, s. 1.)