In the season seven finale, "Hollander's Woods", Castle is confronted with his past when a murder surfaces that matches one he saw in his youth. The murder he'd witnessed had been his inspiration to write as because he was never able finish the story of what had happened in the woods when he was a kid, he became driven to finish all the other stories he could find. The investigation leads them to discover a serial killer who has been operating for at least thirty years with an unknown number of victims, all people who won't be missed. The investigation leads them to the identity of the girl Castle saw murdered and a showdown between Castle and the killer after he breaks into the man's barn in search of evidence. Castle is forced to fatally shoot the killer in self-defense with Beckett's gun and brings closure to his victims though the incident leaves him shaken.