Mass. Gen. Laws ch. 279 § 68
In all cases in which a sentence of death may be imposed, the court shall submit to the jury special questions concerning the issue of murder in the first degree. If the jury determines beyond a reasonable doubt that the defendant is guilty of murder in the first degree, the jury shall specify whether the defendant is guilty of murder with deliberate premeditation, murder with extreme atrocity or cruelty, or murder in the commission or attempted commission of a crime punishable by imprisonment for life, or two or more of these. Upon a verdict of guilty of murder in the first degree with deliberate premeditation, or murder in the first degree with extreme atrocity or cruelty, a presentence hearing shall be conducted, unless the commonwealth stipulates that none of the aggravating circumstances as defined in paragraph (a) of section sixty-nine exists, before the jury before which the case was tried; provided, however, that if in the opinion of the judge presiding at the presentence hearing, it is impossible or impracticable for the trial jury to sit at the presentence hearing, a new jury shall be impanelled to sit at the presentence hearing. The selection of that jury shall be according to the laws and rules governing the selection of a jury for the trial of a capital case. During the presentence hearing, the only issue shall be the determination of the punishment to be imposed. During such hearing the jury shall hear all additional relevant evidence presented by either the commonwealth or defendant in mitigation of punishment regardless of its admissibility under the rules governing the admission of evidence at criminal trials. During such hearing, the jury shall also hear such evidence in aggravation of punishment as is relevant to the statutory aggravating circumstance or statutory aggravating circumstances as defined in said paragraph (a) of said section sixty-nine; provided, however, that only such evidence in aggravation of punishment as the commonwealth has made known to the defendant prior to his trial shall be admissible, and provided further, that said evidence is otherwise admissible according to the rules governing the admission of evidence at criminal trials. The jury shall also hear arguments by the defendant or his counsel or both and by the commonwealth regarding the punishment to be imposed. The commonwealth and the defendant or his counsel shall be allowed to make opening statements and closing arguments at the presentence hearing. The order of those statements and arguments and the order of presentation of evidence shall be the same as at trial. Upon the conclusion of evidence and arguments at the presentence hearing, the court shall instruct the jury orally and shall provide to the jury in writing the statutory aggravating circumstance or statutory aggravating circumstances as determined by the court to be warranted by the evidence, and also any and all statutory mitigating circumstance or statutory mitigating circumstances for its deliberation. The judge shall also instruct the jury to consider any other relevant mitigating circumstance or mitigating circumstances. The judge shall also instruct the jury that they may not find that the penalty of death shall be imposed unless they shall first make a unanimous determination of the existence of one or more statutory aggravating circumstances beyond a reasonable doubt, and make a unanimous determination that the statutory aggravating circumstance or statutory aggravating circumstances outweigh the statutory or other mitigating circumstance or statutory or other mitigating circumstances beyond a reasonable doubt.
The jury shall then retire to determine whether any statutory aggravating circumstance or statutory aggravating circumstances, as defined by said paragraph (a) of said section sixty-nine or any mitigating circumstance or mitigating circumstances, including but not limited to those defined by paragraph (b) of said section sixty-nine, exist. The jury shall further determine whether the statutory aggravating circumstance or statutory aggravating circumstances it finds to exist outweigh the statutory or other mitigating circumstance or statutory or other mitigating circumstances it finds to exist. The jury shall be instructed that: (1) it may choose to find that the penalty of death shall be imposed upon the defendant or (2) it may choose not to find that the penalty of death shall be imposed upon the defendant. The jury, if its unanimous verdict is to impose the penalty of death, shall designate in writing, signed by the foreman of the jury, the statutory aggravating circumstance or statutory aggravating circumstances which it unanimously found existed beyond a reasonable doubt, and that the statutory aggravating circumstance or statutory aggravating circumstances it so unanimously found outweighed any statutory mitigating circumstance or other mitigating circumstance or statutory mitigating circumstances or other mitigating circumstances beyond a reasonable doubt. The process of weighing the statutory aggravating circumstance or statutory aggravating circumstances and statutory mitigating circumstance or statutory mitigating circumstances or other mitigating circumstance or other mitigating circumstances to determine the sentence, shall not be a mere tallying of statutory aggravating circumstance or statutory aggravating circumstances and statutory or other mitigating circumstance or statutory or other mitigating circumstances for the purpose of numerical comparison. Instead, it shall be a process by which the statutory aggravating circumstance or statutory aggravating circumstances and statutory mitigating circumstance or other mitigating circumstance or statutory mitigating circumstances or other mitigating circumstances relevant to sentence are considered for the purpose of determining whether the sentence, in view of all the relevant circumstances in an individual case, shall be life imprisonment without parole, or death.
After the jury has made its findings, the court shall set a sentence in accordance with section seventy.
The declaration of a mistrial during the course of the presentence hearing or any error in the presentence hearing determined on final appeal or otherwise shall not affect the validity of the conviction.
Mass. Gen. Laws ch. 279, § 68