Final answer:
The moment the narrator kills the old man is not explicitly detailed in the provided excerpts. The texts suggest acts of violence and murder, but do not confirm the specific event inquired about.
Step-by-step explanation:
The narrator kills the old man in the text provided from an unknown story. The actual moment of murder is not detailed in the excerpts; however, the context suggests it occurs during a struggle or an encounter with assassins in the darkness of the night. Different pieces of text presented seem to be from various narratives and they allude to violence or murder, such as the killing of an old woman by assassins, or the death of a young man shot through the heart. None of these, however, explicitly detail the killing of an 'old man' by a narrator, which is what the original question refers to. It may be a part of a story not included in the given excerpts.