Final answer:
The coroner may have ruled 'hand unknown' due to social and political pressures or to avoid further unrest or retribution, reflecting the complexities of legal proceedings during times of vigilantism.
Step-by-step explanation:
The reason the coroner may have ruled that Sam Carter was killed by "hand unknown" despite it being clear to others that he was killed by the posse could be rooted in the complex social and political dynamics of the time. Historical context suggests that during periods of high tension and vigilante justice, legal proceedings could be influenced by various factors such as threats of violence, the desire to protect certain community members, or a lack of willingness to confront the perpetrators. In the provided context, it's possible that the coroner faced pressure to deliver a certain verdict, or he might have believed that accurately assigning blame would lead to further unrest or retribution. Therefore, the ruling of 'hand unknown' could be a safer, albeit less truthful, decision.