On a cold January night in 2001, Amityville, New York, became the backdrop for a crime so shocking it read like the script of a mob movie. A devoted friend and beloved gym owner, Alex “Al” Algeri, was gunned down in what police quickly realized was a case of mistaken identity. The true target was Al’s business partner, Paul Riedel. At the heart of the conspiracy: Paul’s wife, Lee Ann, and her lover, Ralph “Rocco” Salierno.

From May 1918 to October of 1919, the Big Easy of New Orleans was the scene of a brutal serial killer. Targeting mostly Italian...