Violence of the Father by Charlotte Raine

How do you catch a serial killer that has the largest possible number of victims and believes God is on his side? Tobias Rodriguez and Lauren Williams desperately search for their second religious killer, who is more violent and more intelligent—a deadly combo--than the last one. When the killer begins to communicate with Tobias through messages directly sent to his home, the case becomes more personal, more urgent, and more demonic.

A Trinity of Death Romantic Suspense Series
Book 1 - Voice of the Spirit
Book 2 - Violence of the Father
Book 3 - Vengeance of the Son