Forty-three years ago, the Zodiac sent one of his most bizarre and baffling clues. Postmarked July 26, 1970, the envelope contained the now-infamous "Little List" letter, which paraphrased the lyrics of the song "I've Got a Little List" from the classic Gilbert and Sullivan musical The Mikado.

As someday it may happen - That a victim must be found - I've got a little list - I've got a little list

The first production of The Mikado was launched in London and opened on March 14, 1885. The musical became a huge success and remains a popular favorite to this day. Set in Japan, the story focuses on Nanki-Poo, the son of the Mikado, and his love for a beautiful girl named Yum-Yum. The couples wishes to marry but they are thwarted by Yum-Yum's guardian and Nanki-Poo's rival, Ko-Ko the Lord High Executioner. Ko-Ko sings the Little List song which describes the torture he will inflict on his chosen victims. A film production of The Mikado was released in 1939. (That same year, the movie CHARLIE CHAN AT TREASURE ISLAND featured a San Francisco killer who called himself "Dr. Zodiac.") In 1974, another suspected Zodiac letter included paraphrased quotes from The Mikado song "Tit-Willow."

The Zodiac's fondness for the Gilbert and Sullivan musical spawned decades of speculation, but the final words of the "Little List" letter became one of the most controversial clues in the unsolved mystery. At the end of the letter, the Zodiac added the hint: "P.S. The Mt. Diablo code concerns radians & # inches along the radians." The killer referenced an earlier letter which claimed that an enclosed map and code would help authorities locate a buried bomb. The map featured an image of the San Francisco Bay Area with a crossed-circle drawn over the peak of Mt. Diablo and the notation "is to be set to Mag. N," an apparent reference to Magnetic North. The code was never deciphered and the map clues remain unexplained.

A decade after the "radians" hint, Gareth Penn declared that he had discovered the meaning behind the Zodiac's clues. According to Penn's theory, the crime scenes at Blue Rock Springs Park and San Francisco formed one radian angle measured at approximately 57.3 degrees. Penn then constructed many theories based on the radian discovery and he eventually claimed that he had identified the Zodiac killer. For many, Penn's radian explanation provided a sensational answer and became the foundation of many more theories about the crimes.

Over time, the myth of the Zodiac's "radian" eventually became a "fact" cited by many who had simply accepted the theory and never attempted to verify Penn's claims. Other theorists have embraced and adapted Penn's radian theory to suit their own purposes. Ironically, most of the individuals who promoted the radian theory were wrong about the basic facts, including the correct locations of the crime scenes in question. Since the correct locations of the crime scenes served as the entire foundation of the radian theory, the failure to accurately locate those scenes meant that the entire theory was wrong from the very beginning.

Forty-three years later, the Zodiac's "radians" clues remain overshadowed by the erroneous theories created by Penn and other promoters of the radian theory. The myth endures, but the facts debunk the radian theory beyond doubt.

Read the ZodiacKillerFACTS article

THE RADIAN THEORY: Mistakes in the Myth-Making