The Rhyme of the Radian: The theory that Zodiac was no ordinary serial killer was soon to be given a quantum boost. Gareth Penn took the radian theory, along with a highly esoteric mathematical analysis of the Zodiac letters and produced some amazing and controversial results.  His curiosity piqued by the radian hint, Penn acquired a sheet of clear plastic and used a protractor and a ruler to draw the radian angle on it. Next, he laid the completed drawing over a map of the San Francisco Bay Area, placing the beginning point of the angle on the summit of Mount Diablo per Zodiac's instructions. He then rotated the lines of the angle until one leg passed through the murder site of Zodiac victim Darlene Ferrin at Blue Rock Springs. What he was looking at chilled his blood. In Penn's words:

"I felt as if a ton of bricks had fallen on me. The other leg of the angle went straight through Presidio Heights in San Francisco where the Zodiac had murdered the cabbie. It was the most shocking experience of my entire life. Instantly, I knew exactly what kind of person he was."

Later experiments with this process conducted by other researchers revealed that the legs of the radian angle (when extended out further from Mt. Diablo) also passed through the site of the Faraday/Jensen murders on Lake Herman Road and through the murder site area of Riverside murder victim Cheri Jo Bates.

~ Excerpt from Labyrinth13: True Tales of the Occult, Crime & Conspiracy, Chapter 9, The Z Files: Labyrinth13 Examines the Zodiac Murders, page 66.

In a book review commentary of Gareth Penn's Times 17, Zodiac researcher Jake Wark states that, "Regardless of whether one buys Penn's accusations, his methods, or his math, he points out a number of truly intriguing phenomena, most notably the radian that connects Vallejo, San Francisco, and Mt. Diablo.  For my money, this is one of the most important aspects of the [Zodiac] case, and it kills me that it's so often marginalized or relegated to footnotes."

~ Excerpt from Labyrinth13: True Tales of the Occult, Crime & Conspiracy, Chapter 9, The Z Files: Labyrinth13 Examines the Zodiac Murders, page 232.

I am often contacted by Zodiac researchers and an array of curious individuals who express an interest in what is perhaps one of the more weird and puzzling aspects of the Zodiac murder case, that being the so-called "radian theory" as originally hypothesized by Zodiac researcher Gareth Penn.  An interesting essay hosted on Jake Wark’s website tells the following story: Some time ago, in an attempt to settle the issue regarding the radian theory once and for all, a group of three Zodiac researchers participated in an exercise that attempted to recreate Gareth Penn's original method and to test his assertion that extending the "legs" of the Mt. Diablo radian on a map of the San Francisco Bay area showed that those lines actually passed through the Zodiac murder sites.  The three researchers, working independently of each other with identical maps and tools, were able to prove that this method did indeed allow them to accurately locate all of the Zodiac murder sites.  It is important to note that these researchers estimated that they were working within a one-degree margin of error in order to take into account the fact that they were using different writing implements, i.e., sharpened pencils as opposed to the blue felt-tip pen that Zodiac had actually used to mark on the original map.  What we are left with, if in fact this hypothesis is true, is the knowledge that the Zodiac murder series may have been premeditated and "designed" to an extent that is very chilling to consider.  The picture that emerges is that of an even more bizarre, cold-blooded and calculating murderer than what immediately met the eye on first inspection.

~ Excerpt from Labyrinth13: True Tales of the Occult, Crime & Conspiracy, Chapter 9, The Z Files: Labyrinth13 Examines the Zodiac Murders, page 232.

The Zodiac Circle Theory: Other Zodiac researchers have taken Gareth Penn’s radian theory and expounded on its merits to a very intricate and compelling degree, going far past his initial observations and clearing up some of the grayer areas.  One of those researchers is Michael F. Cole.  Cole, himself an electrical engineer and computer scientist accustomed to detailed mathematical analysis, discusses his study of the radian clues and proposes an alternative to their meaning in what he calls the “Zodiac Circle Theory.”  In a nutshell, the Zodiac Circle Theory proposes that the killer utilized a Zodiac Circle - a circle segmented into twelve equal 30-degree slices similar to those used by astrologers to represent the twelve signs of the zodiac - in order to choose geographic crime-scene locations.  (Further observations by Cole include the “Quadrants of Method Theory,” in which he theorizes that the Zodiac killer varied the weapons he used based on specific geographical areas that the killer created and assigned a different killing method to).

~ Excerpt from Labyrinth13: True Tales of the Occult, Crime & Conspiracy, Chapter 9, The Z Files: Labyrinth13 Examines the Zodiac Murders, page 68.