The Fourth Deadly Sin by Lawrence Sanders

Excellent read, sadly the fifth and last book in the series. PW: Here is the gripping story of a brutally-murdered New York psychiatrist; ex-cop Edward X. Delaney, who must crack the high-profile case; and the only six suspects: the doctor's own patients. It's a blockbuster with twists and turns that will keep you up nights and suspense that "never lags" (The Washington Post). And it is a crowning achievement - by the man who wears the crown as king of the thriller.