Left for dead : a mystery / J.A. Jance.

Enhanced descriptions from Syndetics:

In this instant New York Times bestseller, not even seasoned detective Ali Reynolds is immune to the escalating drug wars just across the border as two ruthless crimes threaten to bring her face-to-face with a cold-blooded killer.

When Santa Cruz county deputy sheriff Jose Reyes, one of Ali Reynolds's classmates from the Arizona Police Academy, is gunned down and left to die, he is at first assumed to be an innocent victim of the drug wars escalating across the border. But the crime scene investigation shows there's much more to it than that, and soon he and his pregnant wife, Teresa, are both under suspicion.

Ali owes Reyes a debt of gratitude for the help he gave her years earlier. When she's summoned to his bedside at Mercy Medical Center in Tucson, it's impossible for Ali to turn away. Upon arriving at the hospital, Ali finds her good friend, Sister Anselm, is there as well, working as a patient advocate on behalf of another seriously injured victim, an unidentified border crosser who was raped and savagely beaten.

As more bodies begin to pile up, Ali becomes determined to seek justice, even when it becomes impossible to know where the danger is coming from. Fast-paced, tension-filled, and intriguingly complex, Left for Dead is J.A. Jance at her riveting best