Who was the killer in the book far from you?

In the book "Far From You" by Tess Sharpe, the killer is revealed to be the character known as "The Closer," who is ultimately connected to the protagonist's past. The narrative intricately weaves together themes of trauma, friendship, and betrayal, leading to this shocking revelation. The story unfolds as the protagonist, Sophie, seeks to uncover the truth behind the murder of her best friend, which ultimately ties back to her own experiences and relationships.