Instruments of Night by Thomas H. Cook

Thomas Cook is one of today's most acclaimed writers of psychological thrillers, penning hypnotic tales of forbidden love and devastating secrets. Now he has written an unforgettable novel that weaves one man's tortured life with a deadly mystery that spans five decades....
Riverwood is an artists' community in the Hudson River valley, a serene place where writers can perfect their craft. But for all its beauty and isolation, it was once touched by a terrible crime-the murder of a teenage girl who lived on the estate fifty years ago. Faye Harrison's killer was never caught-and now her dying mother is desperate to learn the truth about her daughter's murder.
Enter Paul Graves, a writer who draws upon the pain of his own tragic past to write haunting tales of mystery. Graves has been summoned to Riverwood for an unusual assignment: to apply the art of fiction to a crime that was real, and then write a story that will answer the questions that keep Faye's mother from a peaceful death. Just a story. It doesn't have to be true. Or does it?