Screwed - The D.C. Strangler Case
This is book 1 of the Costigan files.
Victim number seventeen is found naked, strangled and posed at the Washington Monument.
Dan Fuller, a young homicide detective, is sidelined from his first case, tasked with finding a retired detective named Costigan and convincing him to help.
He does, but Costigan is crazy, literally and soon has both of them in more trouble than the serial killer.