At the core of my postwar mystery Devils in Paradise is a secret code, inserted in a rare book stolen by one of America’s former Code Girls. Although I myself have no head for the work, I’ve long been fascinated by the world of code-breaking and especially its unsung female stars. In researching the topic, I discovered that while the coding world tends to operate in service of military and political objectives, cryptanalysis has also helped to identify killers, nab mobsters, and provide valuable evidence in homicide investigations.
Elizebeth Friedman and the Mob
In the 1920s, while Prohibition was in effect in the U.S., liquor smuggling was controlled by New York mobsters working out of ports around the Gulf of Mexico and elsewhere. Their operation involved dozens of vessels, sophisticated radio transmitters and encryption machines. The Coast Guard had intercepted a slew of the smugglers’ coded messages but had no clue how to decipher them. Consequently, cryptanalyst Elizebeth Friedman, who had proven her bona fides during World War I, was recruited to decode the messages.
As a special agent of the U.S. Treasury, Friedman decoded hundreds of the mob’s secret communications and testified in 33 trials. In 1933, she testified against 23 mobsters working out of New Orleans, whose arrests were based on her decoded messages. When the defense questioned her expertise, Friedman explained cryptanalysis using a chalkboard and random code letters, quickly deflating the defense’s argument. News reports detailing her courtroom lesson made Friedman a media sensation.
The Unabomber
Code #1, used by Kaczynski
In the case of Theodore “Ted” Kaczynski, better known as the Unabomber, cryptanalysis helped ensure a guilty verdict and a long incarceration. Between 1978 and 1995, Kaczynski mailed or delivered numerous sophisticated bombs that killed three people and injured many more. Despite being hunted by a massive FBI task force, Kaczynski remained an unidentified at-large suspect for 18 years. The FBI finally discovered his identity after a tipoff from his brother and arrested him at his cabin in remote Montana.
In addition to a live bomb, agents discovered many journals in the cabin, some of which were handwritten in secret codes. Kaczynski, a former Berkeley math professor, had invented two elaborate coding systems, which experts agree would have been impenetrable without keys, or instructions, for solving them. Fortunately for the FBI, because Kaczynski never intended to share his coded musings, he made no effort to hide the keys.
The decoded writings included Kaczynski’s plans for various bomb attacks, and they revealed the delight he felt when an attack succeeded. Later, this stated remorselessness was used against him during sentencing.
The Black Dahlia and Zodiac Murders
Cryptanalysis is at the heart of the recent investigation of the 1947 murder of Elizabeth Short, known as the Black Dahlia, and the Zodiac murders of the late 1960s. The Zodiac Killer, who terrorized the San Francisco area with random shootings, sent the press several coded messages that used a combination of letters and figures. During the initial investigation, only one of the Zodiac’s ciphers was successfully decoded. The Zodiac bragged that his last 13-character message, revealing his real name, would never be decoded.
Elizabeth Short
Over the decades, professional and amateur cryptologists alike tried without luck to decipher the Zodiac’s most tantalizing message. In 2022, the Zodiac’s winning streak was finally broken. After months of exhaustive labor, using his own AI program, Alex Baber, an amateur detective and self-described autistic genius, came up with the answer: Marvin Merrill.
Armed with the Zodiac’s decoded name, Baber then turned to more conventional investigative techniques to connect the name to a person. Unexpectedly, those inquiries led to a man who had been a prime suspect in the 1947 Black Dahlia investigation and who also had sent messages to police. The more Baber dug into Merrill’s documented past, the more it appeared that the Black Dahlia killer and the Zodiac were one in the same.
By 2025, Baber, two cold case police detectives and an amateur cryptologist in Stockholm had compiled enough corroborating evidence, including additional decoded messages, to convince most crime experts that two of modern history’s biggest unsolved cases had finally been solved. And it all started with one 13-character secret message.
Key Reference Sources
“Kaczynski’s Ciphers” by Jeanne Anderson (https://thetedkarchive.com, 2015).
“Killer in the Code: Solving the Black Dahlia and Zodiac Cases” by Michael Connelly (https://killerinthecode.compodcast, 2025).
“The Long Blue Line: Mrs. Friedman—the Coast Guard’s ‘Cryptologist-in-Charge’ and NSC Namesake” by David S. Rosen (https://www.history.uscg.mil, 2022).
A.D. Price is a historical fiction writer, you can find her latest novel here.
