The Suicide Murders by Howard Engel, the first book of his Benny Cooperman series. It's almost a parody of the private detective genre which may or may not have been the author's intent. The cover art isn't much, but I've concluded it's an African tribal sculpture, normally posing as office artwork, but also sturdy enough to bash in the skull of a crooked psychiatrist on page 60, so I've scored it in the weapon on the cover category hard mode.