In 2023 the true crime author Mark Dapin published a biography of Karlson titled Carnage: A Succulent Chinese Meal, Mr. Rent-a-Kill and the Australian Manson Murders that also explores his connections to other criminals. The book also revealed that Karlson was an admirer of Adolf Hitler and Nazism who would "indulge his Nazi fetish", use the expression "Two Heil Hitlers" instead of "three cheers" and had a car decorated with a swastika on his lawn. On at least one occasion he threw a party at his home to celebrate Hitler's birthday.

huh, well that's a bummer