Thrill of the Kill (2006)

Brilliant New York crime author Graydon Jennings accepts to help Kelly Holden investigate her sister Allison's murder, which seems uncannily equal to one his anti-hero-lead character Carlton James's kills for the thrill. In the sisters' Vermont home, starting from her diary, they come up with a theory Senator Darren Hartford sent the murderer to keep his adultery covered up. The sting of the tale is in the tail, for several parties.