The Collector by Nora Roberts

The Collector - Freelance writer and professional house-sitter Lila Emerson likes to watch people and makeup stories about their lives.  One night as she watches from the bedroom she is currently using, she sees a woman pushed out a window.  After she gives her statement at the police station, the brother of the man accused of the murder, Ashton Archer, asks her to join him for coffee at a local cop hangout.  Archer, the oldest son of a rather large family, convinces her that his brother is not responsible.  Furthermore, Lila and Ash become friends.  Meanwhile, the real killer is following both of them to determine if they know anything about the murder as well as the location of the item the killer was hired to find.