Guarding Light by Cate Mckoy‏

Jack Gard and Catlyn Lyte become friends in high school. Although he cares for Catlyn, Jack refuses to get into a relationship with Catlyn, due to her age. 
Then Catlyn is raped and her world is torn apart when Jack sides with his best friend. Devastated, Catlyn flees Newburgh, NY. 
25 years later, someone is raping and killing young black females in Jack Gard, Chief of Detectives’ hometown. Working against an escalating killer, Jack requests help from a special division of the FBI. ...