Coyote

For the sake of an illegal immigrant, Boston private investigator and part-time taxi driver Carlotta Carlyle gets involved in a serial murder case
Six-foot-tall, redheaded ex-cop and Boston-based private eye Carlotta Carlyle is "the genuine article: a straightforward, funny, thoroughly American mystery heroine" (New York Post).
Carlotta Carlyle has just returned home when a dead woman walks through her door. Manuela Estefan is breathing, walking, and talking—but according to the newspaper in her hand, she was just found savagely murdered in a marshy park not far from Fenway. The deceased woman was carrying Manuela's ID card, and Manuela now begs Carlotta to get it back. Boston PIs aren't supposed to touch murder cases, but when Carlotta comes back from the kitchen with a glass of water, Manuela has vanished, leaving five crisp hundreds on the table as a silent plea for help.

But this is no ordinary murder case. The woman holding Manuela's ID is only the first victim in what will prove to be a series of slayings carried out by a vicious maniac—someone who preys on Boston's immigrant community, but who would not be above going after a tall, red-headed private eye.
Coyote is the 3rd book in the Carlotta Carlyle Mysteries, but you may enjoy reading the series in any order.