The Last Sinner by Lisa Jackson

There are killers so savage, so twisted, that they leave a mark not just on their victims, but on everyone who crosses their path. For Detectives Bentz and Montoya, Father John, a fake priest who used the sharpened beads of a rosary to strangle prostitutes, is one such monster.
Bentz thought he’d ended that horror years ago when he killed Father John deep in the swamp. But now there are chilling signs he may have been wrong. A new victim has surfaced, her ruined body staged in deliberate, unmistakable detail. Either it’s a terrifying copycat, or Father John, the detective’s own recurring nightmare, has come back to haunt New Orleans.
Another death, and another. Bentz is growing convinced that Father John isn’t just back. He’s circling closer, targeting those Bentz loves most.
And this time, he won’t be stopped until the last sinner has paid the ultimate price…