Did Nazi dictator Adolf Hitler amass a fortune that he hid in secret bank accounts? According to a new British documentary, Hitler died a billionaire. British program "The Hunt for Hitler's Missing Millions" claims that at his peak, the net worth of the Nazi leader could have hovered around 1.1 billion Reichsmarks, or $6.1 billion today. He made his money, among other ways, from royalties on his book "Mein Kampf," the printing of his image on stamps, and public appearances and lectures. The documentary claims that Hitler may have owed some 400,000 Reichsmarks ($3 million) in back taxes. Estimates about Hitler's fortune started to surface shortly after his death after the discovery of his secret will by a German Jew who worked in British intelligence. Herman Rothman, today in his 90s, told the documentary makers that after Hitler's suicide on April 30, 1945, the counter-intelligence unit operating against the Nazis identified a man in civilian clothes in Berlin who, they believed, was a Nazi on the run. One of Rothman's colleagues noticed a strange stitch in that man's clothing. Inside, he discovered the deceased dictator's will. According to Rothman, part of the document referred to Hitler's assets, showing he had been an "a shrewd manager of cash with a love of money."