Final answer:
The rigor mortis present in the face, neck, arms, and torso suggests the runner has been dead for approximately 12-24 hours, although external factors can affect this estimation.
Step-by-step explanation:
The time of death can be estimated using signs such as rigor mortis, the stiffening of the muscles after death. Rigor mortis generally begins within 2 to 6 hours post-mortem and can last up to 48 hours. Given that rigor mortis in the scenario presented affects the face, neck, arms, and torso, these findings suggest the individual has been dead for approximately 12-24 hours. This window is based on the typical progression of rigor mortis, which usually starts in the smaller muscles of the face and neck before spreading to the larger muscle groups. However, factors like temperature can accelerate or decelerate the process, so the estimate can vary.