I'd like to shine a spotlight on The Irises by Cynthia Lott. This book is the second in the Southern Spectral Series.
From the back cover:
In 1979 New Orleans, detective Roy Agnew is thrown into another murder investigation. Re-entering the world of the supernatural, he realizes that he may be the only person able to stop a killer. In order to catch a paranormal murderer, Roy must rely on the one thing he struggles with the most: his faith.