Detective by Arthur Hailey

Serial killer Elroy "Animal" Doil is hours away from the electric chair. In his last hours of life, he wants to make a confession- to detective Malcolm Ainslie, the man who put him away. And as much as he'd like to, Ainslie can't ignore the criminals request. Beacuse Doil is guilty of a gruesome double murder, his confession could close ten other unsolved slayings.
What Ainslie learns, however will thrust him into an investigation that leads directly to elite levels of city government- and some of his trusted collegues.....