A German Requiem — Philip Kerr

Bernie Gunther had his first brush with evil as a policeman in 1930's Berlin and came to know it intimately as a private eye under the Nazis, when each case drew him deeper into the enormities of the regime. Now the war is over and Gunther's in Vienna, trying to clear an old friend of the murder of an American officer. Amid decaying imperial splendor he traces concentric circles of depravity that lead him to a former head of the Gestapo.