Trainor, a firefighter, entered a burning building in an effort to rescue people who were believed to be trapped inside. While inside the building, Trainor suffered from heavy smoke and heat and had trouble breathing through his face mask. Trainor collapsed while on the roof of the building and was taken to a hospital, where he was pronounced dead on arrival. Rhoades (defendant) was charged with arson for setting the fire and with second-degree murder for causing Trainor’s death. At Trainor’s trial in Superior Court, a medical expert for the Commonwealth (plaintiff) testified that Trainor died from coronary thrombosis brought on by cold weather, stress, and smoke inhalation. The trial judge instructed the jury that Rhoades could be convicted if his act in setting the fire was either a contributing cause or part of the proximate cause of Trainor’s death. Rhoades was convicted on both counts and appealed his murder conviction to the Supreme Judicial Court of Massachusetts.