The five most popular questions about the story content of Gone Girls: The Long Island Serial Killer, season 1, episode 1, excluding overall plot and ending, are:

1. Who were the victims and what were their backgrounds, especially Shannan Gilbert's story?
2. How did the investigation unfold and why were the murders unsolved for nearly 20 years?
3. What role did police corruption and investigative failures play in delaying justice?
4. How did a pivotal tip finally lead to an arrest, and what new details emerged about the killer?
5. How are the victims' families portrayed in their resilience and pursuit of justice throughout the series?

These questions arise from the series' focus on victim stories, investigative challenges, police corruption, and the eventual breakthrough in the case, as highlighted in reviews and episode descriptions.