I have finished Tartt's novel. I have read it at least five times, and I find it really fascinating each time. Perhaps it's because the book has a certain gloomy atmosphere, or because I like its interpretation of friendship, or simply because Tartt has a very good sense for the psychological side of the act of murder. I enjoy her digging deep into the human mind as I loved Dostoyevskiy's Crime and Punishment. Papen is in a way a Raskolnikov - as once Tartt herself refers to the famous sentence, when Raskolnikov confesses his murder.
"It was I killed the old pawnbroker woman and her sister Lizaveta with an axe and robbed them."
And I think the reader is finally left on their own to decide what a murder is. Why does a group of well-educated young people want to commit this deadly sin? It's irreversible, and it is going to hang over their heads forever. The murder of a friend - this is the act which carries on what Raskolnikov began. Papen and his friends - despite their obvious love to each other - push a friend into a ravine. This act stays with them forever, and prevents the protagonist from leading a happy life.
I always feel an attraction towards these kinds of novels which deal with the dark side of the human soul. I love the unsolvable misteries that arise from the unknown depth of the mind. I still wonder about these secrets. It's really a Secret History.