Final answer:
The observations that led the narrator to believe that Uncle Otto murdered his partner are not provided in the given passage.
Step-by-step explanation:
The observations that led the narrator to believe that Uncle Otto murdered his partner are not provided in the given passage. In order to answer the question accurately, I would need more information or context from the text. It is important to carefully analyze the details and clues provided in the story to form a conclusion about Uncle Otto's actions.