## Facts

- After a party involving alcohol and marijuana, Adam Rosier left in a car with sixteen-year-old Kristal Hopkins; a witness said both appeared intoxicated.
- The next day, Hopkins was found in a state forest barely alive, partially clothed, and covered with blood; she died shortly after reaching a hospital.
- Physical evidence at the scene included skid marks and debris consistent with a vehicle striking an object; Rosier had been driving a Mercury Capri (a Ford product).
- The medical examiner concluded Hopkins suffered extensive blunt-force injuries consistent with being struck, run over, and dragged by an automobile, including in more than one direction.
- Investigators examined Rosier’s vehicle for damage and biological material.
- A forensic laboratory performed PCR-based short tandem repeat (STR) DNA testing; biological material from Rosier’s car matched the victim’s DNA profile, and statistical testimony accompanied the match.
- The prosecution also presented testimony that Rosier made inculpatory statements to others, including admissions consistent with hitting or running over the victim with his car.

## Issues

1. Whether PCR-based STR DNA testing was sufficiently reliable and generally accepted to be admissible as scientific evidence.
2. Whether DNA match statistics computed using the product rule and the laboratory’s population database were reliable and admissible.
3. Whether the judge erred by refusing to give a special jury instruction focused specifically on DNA evidence.
4. Whether the jury instructions adequately explained the relevance of intoxication to deliberate premeditation, malice, and extreme atrocity or cruelty.
5. Whether the evidence supported first-degree murder and whether extraordinary relief was warranted on plenary review in a capital case.

## Decision

- The court affirmed the conviction of murder in the first degree on theories of deliberate premeditation and extreme atrocity or cruelty.
- The court held PCR/STR DNA evidence was properly admitted because the methodology was shown to be scientifically reliable and generally accepted when performed under appropriate protocols.
- The court upheld admission of the DNA statistical testimony, including product-rule calculations, concluding the methodology was reliable on this record and defense criticisms primarily concerned weight.
- The court found no error in declining to give a specialized DNA instruction; standard instructions on expert testimony and the Commonwealth’s burden of proof were sufficient.
- The court held the intoxication instructions correctly stated the law and adequately directed the jury on how intoxication could affect the required mental states.
- After independent review of the whole record in a first-degree murder case, the court declined to reduce the verdict or order a new trial.

## Legal Principles

- Novel or developing scientific evidence may be admitted when the proponent shows scientific reliability and general acceptance in the relevant scientific community, applied with appropriate laboratory protocols.
- PCR-based STR DNA profiling may satisfy admissibility standards when supported by expert testimony addressing methodology, quality controls, and the adequacy of supporting databases.
- DNA match probability evidence may be admitted where accepted population-genetics assumptions are supported and the product rule is properly applied; disputes about database size or assumptions often bear on evidentiary weight rather than admissibility.
- Trial judges have discretion over the need for specialized jury instructions on particular scientific evidence; general instructions on evaluating experts and proof beyond a reasonable doubt can suffice.
- Evidence of intoxication does not excuse criminal conduct but may be considered in determining whether the prosecution proved specific intent and other mental-state elements beyond a reasonable doubt.

## Conclusion

The court upheld Rosier’s first-degree murder conviction, concluding that PCR/STR DNA testing and product-rule statistical evidence were admissible on the record presented, that the jury instructions on DNA evidence and intoxication were legally adequate, and that the overall evidence supported the verdict without warranting extraordinary relief on plenary review.


Commonwealth v. Rosier, 425 Mass. 807, 685 N.E.2d 739 (Mass. 1997)