The Zodiac Killer Z32 Cipher and the Rule of Three
On November 25, 2014, a user identified as Mr. Lowe initiated a forum thread titled Zodiac Month Clock Theory on a now-defunct website formerly operated by Mike Morford. In this thread, Mr. Lowe interprets the Zodiac's crosshair symbol found in the November 9, 1969, letter - crosshair annotated with five X’s - by assigning each X to a calendar month.
From this framework, he identifies links to a
historical scientific advisory group known as JASON. Prior to encountering this
thread, I was unfamiliar with the JASON organization and consequently undertook
independent research to better understand its origins, structure, and purpose.
That inquiry led me into broader topics, including Alfred Loomis, the
development of microwave radar, and the history of aerial navigation. Some of
the information I encountered is relevant to what follows.
During an exchange with Mr. Lowe, he questioned my reference to a “4-inch” measurement. I clarified that I believed the Zodiac's crosshair on the Phillips 66 map he provided - marked with the numerals 3, 6, and 9 - was constructed to scale using the reference scale printed on the bottom of the Phillips 66 map. It appears the Zodiac may have employed a circle template, rendering a symmetrical crosshair with a diameter of approximately four inches.
In either event, the measurement (inches or miles) prompted a key realization: the intended location of the supposed bomb described in Zodiac’s June 26, 1970, letter was likely confined to the boundaries of the provided Phillips 66 Map:
Though it might initially seem improbable to
determine a precise terrestrial location based on the materials, it becomes
more plausible when considering the possibility that both the map and the code
are meant to draw attention to observable elements - such as towns or landmarks - already printed on the map. The critical questions thus become:
1.
What are we meant to observe?
2.
How do we identify it?
3.
And why are we being guided there?
In addition to the "4 miles," the placement of the crosshair
over Mount Diablo by the Zodiac merits close analysis. Historically, Mount
Diablo has served as the site of two distinct survey markers. The first,
established by Ransome of the Geological Survey, was part of a broader
initiative to classify lands, geological formations, and mineral resources.
This inland-focused survey mark is located approximately twelve miles from the
point Zodiac appears to have utilized on the Phillips 66 map.
The second survey point is located at the summit’s octagonal rotunda, which houses a
large compass. Beneath this compass lies a foundational survey mark installed
by General Richard Dominicus Cutts of the United States Coast Survey. This organization,
established in 1807 by Thomas Jefferson (whose image notably appeared on
Zodiac’s stamps used for the December 20, 1969, communication), was originally
tasked with charting the coastlines and maritime boundaries of U.S. territories.
Prior to the rotunda's construction, a 75-foot
Standard Oil tower and navigational beacon stood at the same site. Constructed
in 1928, the tower was funded in part by the Department of Commerce to aid both
maritime and aviation navigation. One of its primary users was the U.S. airmail
system, which, like the concepts of flight and aircraft, recurs in Zodiac's
communications - either explicitly or obliquely.
Given that the crosshair is anchored at a site
historically used to survey the coastlines and that the Phillips 66 map shows
land predominantly south of San Francisco Bay, San Pablo Bay, and the Carquinez
Strait, a logical hypothesis is that the target location lies within or just
south of San Francisco and Contra Costa County. This assumption becomes crucial
when evaluating the data that follows.
Multiple theories have been proposed to
explain why the Zodiac used a crosshair marked with five X’s in his first bomb
letter dated November 9, 1969. While these interpretations vary, a consistent
theme involves overlaying this crosshair on Mount Diablo and adjusting it for
magnetic declination. Given that the crosshair appears in a bomb-related
letter, this orientation seems appropriate.
To explore this further, I overlaid Mike
Cole’s magnetic declination grid, which is segmented into 30-degree intervals,
onto the Phillips 66 map, centering it at the point Zodiac indicated
on Mount Diablo. Before applying the overlay, I removed any of Cole’s auxiliary
lines that were unrelated to the essential numerals - 3, 6, 9 - or to the five
X’s as shown:
The resulting visual alignment reveals three significant locations - airfields - that align with crosshair points 6, 8, and 10 when rotated to magnetic north:
1. Buchanan Field Airport (37.5923 N, 122.0325 W)
2. Alameda Naval Air Station (37.7861 N, 122.3186 W)
3. Moffett Federal Airfield (37.2454 N, 122.0254 W)
These airfields, when contrasted with other
crosshair vectors such as 0, 3, 9, 7, and 11 - which point to areas outside the
scope of the Phillips 66 map - become especially relevant. Their inclusion
supports the idea that Zodiac’s intended references are constrained to
locations visible on the map and possibly tied to aviation and navigation
systems.
This realization brought me back to Alfred
Loomis and the evolution of navigational technologies, specifically microwave
radar and Doppler/omega/VOR systems. I was curious about how radians might
factor into this, and I revisited the "4-mile," scale, speculating whether that might be a clue.
However, to progress, we must rectify why the Zodiac felt the need to draw two crosshairs abnormally large in the July 26, 1970, letter - Here and Here. We can see that the latter one is tied explicitly to the map and code by the added statement: "Ps. The Mt. Diablo code concerns radians + # inches along the radians".
If we take the San Francisco Police 1-inch Ellison ruler seen in the high-resolution images of the Zodiac communications and measure each crosshair, we find that the first crosshair with the bold 0 and = 13 notation measures approximately 3-11/16 inches. The second crosshair, containing the notation about the use of radians, measures approximately 3-13/16 inches. Due to minor differences in drawing or printing, one circle was measured along its width and the other along its length to account for slight elongation, producing nearly matching sizes of what would appear to be a desired 4-inch diameter.
So, what does this all mean?
On the map itself, the crosshair was drawn to a scale that aligns with the “4” mark on the scale bar. This scale bar is labeled in miles, meaning the number 4 represents 4 real-world miles. The corresponding physical measurement on the map is approximately 0.625 inches (5/8 inch).
This crosshair serves as a precise, cartographically accurate representation: it allows readers to directly use the scale bar to understand the actual size of the area in miles. The Zodiac adhered to the true scale here, ensuring that anyone measuring directly with the bar would see exactly 4 miles in real-world distance.
This small crosshair is subtle, but it’s critical - it grounds the map in real-world distances and provides the foundation for the conceptual leap that follows.
Separately, the Zodiac also provided the two larger circles that measure roughly 4 inches in diameter. At the map's stated scale of 1 inch = 6.4 miles. each of these circles would represent: 25.6 miles.
They are meant to visually emphasize a navigational framework, making it easier to measure angles, plot bearings, and test distances. When scaled using the map’s ratio (1 inch = 6.4 miles), the 4-inch crosshairs span approximately 25.6 miles - far larger than the original 4-mile map crosshair. This size difference is intentional and practical: it allows users to apply geometric relationships to the map, identifying alignments or intersections that reveal meaningful positions relative to Mount Diablo. In this sense, the crosshairs function as tools for spatial orientation rather than literal markers.
At this point, it becomes necessary to scale the Phillips66 crosshair to 4 inches on the map to perform any geometric or spatial calculations that may be waiting.
All of the above led me to study navigation principles, specifically trilateration, which is a method used to determine a location by measuring distances from three known points. Unlike triangulation, which relies on measuring angles, trilateration uses circles drawn around each reference point, with radii corresponding to the measured distances. The unknown location - the so-called “fix” - is found where the circles overlap (shown in red):
Applying this concept to the three airfield locations and Mount Diablo, overlapping circles form. Moffett Field, being further south, intersects only minimally and does not contribute to a meaningful fix. The remaining three circles - Buchanan Field, Alameda Naval Air Station, and Mount Diablo - overlap significantly, creating a clear intersection zone.
While the map labels it simply as “St. Mary’s College,” the institution’s full name is Christian Brothers St. Mary’s College. The map alone - combined with Mount Diablo as a datum, the crosshair with five X's, declination, and observable landmarks - is sufficient to identify a fix-point via trilateration.
The 32-symbol cipher, by contrast, likely serves a secondary role: it could validate the map-based location, provide stylistic or performative emphasis, or simply act as a distraction. Because the cipher is relatively short, there are multiple plausible ways the name or phrase could have been encoded, preventing it from independently pinpointing precise coordinates. For example, Zodiac could have inserted nulls or filler symbols between the real letters; if the plaintext is 16 characters long, including punctuation (“ST.MARY'SCOLLEGE”), adding a null between each letter would double the length to 32 symbols, making the cipher appear more complex while still encoding the intended message.
Similarly, each plaintext character could have been represented by two symbols, or repeated sequences, extra characters at the start or end, or other forms of padding could have been added to create symmetry. Finally, Zodiac might have stylized or compressed the full institution name, treating the cipher as a performative or aesthetic device rather than a strict cryptographic tool.
Any of these methods could allow the cipher to confirm or “validate” the map-based fix without providing new information. Essentially, the cipher would communicate: “Yes, the map solution is correct,” while creating the impression of greater complexity or secrecy. In this way, Zodiac’s layered design relies on the map to supply actionable information while the cipher reinforces or embellishes the solution, adding conceptual depth without being essential to geolocation.
Notably, this interpretation does not require advanced cryptographic operations, radian calculations, or other sophisticated mathematics. Rather, it highlights how Zodiac’s conceptual device guided observers to recognize spatial relationships on the map, combined with his knowledge of naming conventions and language, to craft a narrative riddle. The precision with which he constructs this illusion further supports the idea that he possessed formal education - perhaps in English or a related discipline - and used that knowledge to manipulate both public and investigative attention.