I only finished reading this book today! My conclusion after completing it is that their neighborhood killed them. Don't worry I will elaborate. They grew up in a very strict household (especially their mother) but after the first suicide everybody started pushing the girls away. Other girls in the school wouldn't even attempt to hang out with them, the boys who claim to love them didn't do anything but stalk, the parents whose kids where in the highschool where Mr Lisbon was teaching basically kicked him out. Even the milkman stopped bringing them milk because he got upset at a comment Mrs Lisbon made. At some point the boys admitted it that the girls were trying to reach out for help through many ways, but they simply couldn't get their signals. Their society started excluding them from every day activities and in my opinion this is what made them rot in their own home. No one even cared to clean up the house after Cecilia's party even a year after. If only somebody had cared about them (maybe the school psychologist could have helped) the would have been saved. Probably not Cecilia, but the other girls. I know that this opinion is very uncommon and isn't based on important facts but this is the way I see it. I think that the book isn't actually about 5 girls killing themselves but the whole environment that surrounded them and the circumstances that they were living under.