How is the world is the case not solved in hours? One surviving kid from a set of normal nice parents. Do those parents not have jobs, a single friend, any other family, a single neighbor who realizes “huh, they aren’t around anymore?” I feel any neighbor on the street figures out something is up, much less detectives and FBI agents being stumped for what, a month?!
ETA: I actually liked a lot of the movie and enjoyed the watch. But I couldn’t stop thinking about this the moment it became clear the parents went comatose before the event so would clearly not be good for questioning which would be a massive red flag to any investigation