Lawrence Block 
In the Midst of Death [EPUB ebook] 

Bad cop Jerry Broadfield didn’t make any friends on the force when he volunteered to squeal to an ambitious d.a. about police corruption. Now he’saccused of murdering a call girl. Matthew Scudder doesn’t think Broadfield’s a killer, but the cops aren’t about to help the unlicensed p.i. prove it — and they may do a lot worse than just get in his way.