The Crush by Sandra Brown

After she unwittingly frees a dangerous contract killer, a surgeon reluctantly joins forces with a tenacious detective obsessed with taking down their enemy at all costs.
As a surgeon, Dr. Rennie Newton is the consummate professional. When she's summoned to jury duty, she brings competence and composure to the courtroom - a skill she learned while performing surgeries. It is this commitment to precision that compels her to deliver a not guilty verdict in the murder case against notorious contract killer Ricky Lozada.
It will be the most regrettable decision of her life. When a rival colleague is brutally slain, Lozada's menacing shadow looms over the murder, but the investigators pinpoint Rennie as the prime suspect. Soon, the police begin violating the privacy she has cultivated and protected at all costs. And when Lozada begins an earnest courtship, it becomes terrifyingly clear that he is obsessed with having her.
Wick Threadgill is a detective on indefinite leave from the Fort Worth PD with a very personal agenda for the contract killer. Temperamental, bitter, and driven by loyalty and love, Wick is determined to destroy Lozada. In order to defeat him - and save their own lives - Rennie and Wick form an uneasy alliance.
Mistrustful of each other, they know only one thing with absolute certainty: like one of Lozada's prize scorpions, they won't see it coming when this killer strikes. The Crush will take you on a tortuous path through a twisted sociopath's eerie obsession, a haunted man's fragile hopes for redemption, and a woman's heart as she struggles to face her greatest fear: to open herself to love.