Answer:
Because he wants to reinforce the seriousness of the theme presented in the story.
Step-by-step explanation:
"Nothing but the truth" is a novel that deals with the subjectivity of truth and how a person's statements, when analyzed in individual interpretations, can represent the same event in different ways and corrupt the truth about what actually happened. The author of the story, takes this theme seriously, mainly because of the results it can cause in a person's life, for this reason, he decides to end the story on a serious note, which emphasizes the seriousness of the theme explored in the story.