Original post from 2020 (link)
On March 19, 2019, the first version of this solution dating back to 2018 (mentioned here) was attached by me as a supplement of the denunciation against “Joe Bevilacqua”.
A few months later I also posted an updated version on Reddit.
“FOOTHILL BLVD HILLCREST 14 MI FAR 570°” may be the decryption of the “Mt. Diablo code,” the 32-symbol cipher at the bottom of the Zodiac Killer’s letter postmarked June 26, 1970.
The 2018 decryption has undergone slight changes. In the last review (2023) I went from “16” to “14 miles.”
Thanks to Reddit user VT_ Squire for having helped me improve the explanation (unwittingly).
To scroll down the page and go directly to the full explanation click here.
In addition to indicating where he set a bomb, Zodiac provides a distance without decimals, 14 miles, and the size of an azimuth, a 570° angle, i.e 210° plus a round.
It is the route to follow from the top of Mt. Diablo to the target zone, which is located in the town of San Leandro. To determine it, the author of the cipher applied the classic method for navigation with compass and map .
- The angle is calculated starting from Zodiac’s 0 because the vertical axis of the compass is not perfectly pointed towards true north (it is at + 2°).
- The map scale is wrong. The actual distance is about 16 miles, as I previously wrote.
- I had thought that there might be “fro” (from) instead of “far”, but in the end I discarded it.
Zodiac wanted to complicate the decryption by adding 360° to the azimuth.
The azimuth is the angle expressed in degrees (“570°” in this case) between the magnetic north at which the compass needle originally points and the imaginary straight line to follow to reach the point indicated on the map (as the one in the image above).
How to solve the cipher
On June 26, 1970, Zodiac sends a letter with his last known cipher.
Zodiac’s letter – June 26, 1970
Attached map
Zodiac’s tip – July 26, 70
Zodiac enclosed with the letter a Phillips 66 map of the San Francisco Bay Area. There is a compass drawn indicating true north on it (next image).
The serial killer claims that the cipher, combined with the map, will tell readers where he set his bomb.
Zodiac was capable of setting up complex ciphers.
According to the Army Security Agency, he probably had military training in cryptography (next image).
This means that the serial killer knew that it would be unlikely to solve this short cipher with only three symbols (out of 29) repeated a couple of times. Even a few explicit hints in this letter and a subsequent one are not enough:
- combine the cipher with the map;
- turn the compass needle toward magnetic north;
- the solution involves “number of inches” and “radians,” the measurement of a distance and an angle.
In 2018, I thought that Zodiac might have hidden another useful tip to solve the encrypted text in the letter or map.
I spotted it in the arrow-shaped compass needle and the presence of segments that divided the quadrants.
I said to myself:
"Maybe by connecting these segments and the compass needle I will get the distance from the top of Mt. Diablo to the target area?"
By aligning the segments that divide the quadrants and rotating the final arrow, the possible alternative solutions are delimited to the perimeter of 3/4 of a circumference.
There is no longer a huge area to check to exclude alternative locations to a possible solution, but only those that can be reached by the final arrow.
This way you can compare possible targets with Google Maps and find the “Eden Township” Alameda County Sheriff’s Station in San Leandro.
The place where the bomb would have been “set” is an area between the street where the building is located, Foothill Boulevard, and a neighboring zone, Hillcrest.
This solution is suggested by Zodiac’s previous letter postmarked “April 20, 1970”, where he calls a policeman killed with a bomb a “blue meannie” (sic).
The “blue meanies” are the enemy forces fighting the Beatles in “Yellow Submarine”.
On February 3, 1970, the New York Times informed that 12 Alameda County deputy Sheriffs had been charged for civil rights violation.
The news article recollects that after demonstrations in the ’60s the Alameda County Sheriff’s forces were nicknamed “blue meanies” by Berkeley protestors. It reads:
"The Alameda County Sheriff's forces have seen duty at these demonstrations and picked up the nickname “the Blue Meanies” from Berkeley radicals."
On the following March 24, the Napa Register reads that the deputies charged with civil rights violation received a financial aid by a group of citizens in a ceremony held in the same Sheriff’s substation in San Leandro that Zodiac seems to have targeted.
The cipher “is about” inches and radians, in fact it contains a distance given by the sum of the segments of the compass (expressed in miles), as well as the angle (in degrees) of the direction to follow from the top of Mt. Diablo to the target, with a calculation based on the indications of Zodiac.
The solution containing degrees and miles and the suggestion to set the compass needle towards magnetic north refer to the classic method used to move with the compass from one point to another on a map.
The “arrow” system could allude to the “Let the sunshine in” method I applied in deciphering Zodiac’s name.
Far
Zodiac’s use of “far” could be intentional. He already made mispellings and lexical errors in his notes that appear to be deliberate. To name two, in the same note where he declares that he did not kill a policeman with a bomb, he writes “cid” instead of “kid”; “cerous” instead of “curious”.
Full explanation
The author of the message claims that the cipher indicates the place where he set a bomb. In letters he mailed to the San Francisco Chronicle in the previous months, he already threatened to explode a bomb along a road to “wipe out” a schoolbus.
Zodiac provides some information:
- The bomb no longer is aimed to kill schoolchildren;
- The cipher and the map are complementary to know the place where he would have placed the bomb;
- On the map there is a drawing of a circle divided into quadrants with an arrow that “is to be set to mag. north” (a compass, therefore);
- In a letter sent a month later, he writes that the solution has to do with radians and “inches along radians,” measurements that indicate an angle and distance.
Step 1: the compass needle
To arrive at the solution, you need to guess first that you need to align the segments of the compass drawn by Zodiac and rotate the needle.
What is obtained is the possible distance on the map, composed of the sum of the lines, from the top of Mt. Diablo to the place chosen by Zodiac.
This is my interpretation of the phrase “inches along the radians”.
The direction remains to be found.
Step 2: degrees
If the cipher contains the measurement of an angle and a distance, you may find a symbol of a unit of measurement at the end.
Degrees, not radians, are normally used to calculate a route with a compass.
The degree symbol is a sort of small “O”. So I supposed that in the plaintext there was a measurement in degrees and that Delta replaced an O.
Step 3: map
You must rotate the compass needle and check on a map (Google Maps) which places are consistent with the repeated symbols.
After some time, and various combinations, I found an area compatible with the first part of the solution:
"FOOTHILL BLVD HILLCREST"
I noticed the presence of the Alameda County Sheriff’s Station “Eden Township” along Foothill Boulevard at Hillcrest Knolls in San Leandro, an area about 14 miles and decimals (16 miles and a half actually) away from the top of Mt. Diablo.
The distance is not correct because the map scale is.
Once the area was selected, I measured the angle between the top of Mt. Diablo and the target following Zodiac’s instructions.
I realized that the Zodiac compass needle was inclinated 2° degrees to the east (an error, I believe). Therefore, it was necessary to measure the angle with respect to the tilted axis of the needle and not the vertical axis of the map.
To do so, I used Paint 3d (see next chapter).
As requested by Zodiac, I positioned the needle along the axis of magnetic north, which in the San Francisco Bay Area at the time of the letter was at +17° (source).
I then measured the remaining angle, i.e. the azimuth, which was +210° (based on the Zodiac needle).
I added 360° to the solution and noticed that the replacements of numbers with letters of the Latin alphabet followed the reverse alphabetical order W → N = 0 → 9 (second image below).
Of course 570° is a mokery, i.e. a “presa in giro” in Italian (giro means “round”), given that Zodiac could easily have written 210° without adding other 360°.
Verifying the solution
The angle and the distance indicated by Zodiac’s compass can be checked out using this image.
It is possible to rotate the compass needle with Paint 3d.
Attention! To count the degrees, the Zodiac compass must be turned as it is, without straightening it, because the author did not draw it perfectly perpendicular (but 2° to the East).
If you intend to use a simple vertical line instead of the compass, you must point it 2 degrees East before starting the count.
Once the pointer has been “stretched” by adding along its axis one after the other the lines drawn by Zodiac dividing the quadrants, the arrow will indicate precisely the same area-target obtained in the decryption, that in full is:
"FOOTHILL BLVD HILLCREST 14 MI FAR 570°"
Where “far” instead of the correct “away” is probably an intentional error by the author of the message, who made similar ones in his notes.
Degrees
Zodiac writes that the solution “concerns” radians and inches, without specifying whether they are in the plaintext.
The solution contains degrees which, like radians, measure the size of an angle.
Normally on compasses there are degrees, not radians, which serve to identify the direction to follow towards the place to be reached. In this case, the place of the bomb.
In an article in ’81, researcher Gareth Penn observes that Zodiac inserted numbers that were multiples of 3 instead of the cardinal points, which is compatible with a solution containing degrees (those of a circumference are 360).
A presa in giro
Of course 570° is a a joke, i.e. a “presa in giro” (giro means “round” in Italian), since Zodiac could easily have written 210° without adding another 360°.
Probably, it serves to complicate the decryption.
“Mi far” or “miles”?
The FBI analysts in 1970 supposed the presence of the word “miles” in the text (FBI Vault – Zodiac, part 5, pp. 167 – 168; picture below).
Strenght points
The Mt. Diablo code is composed of 32 characters. Only three are repeated (just once). It means there are 29 different symbols.
How can it be proven that the solution is the right one?
There are eight strenght points that support the outcome of the decryption.
1. First of all, the method is prescribed by Zodiac himself in the Mt. Diablo letter and in his tip of 26 July 1970. He wrote that:
A) to find the bomb the code must be “coupled” with the map.
B) the arrow in the circle divided into quadrants drawn on the map “is to be set” to magnetic north (why?);
C) the code “concerns” (not “contains”) “radians & # inches along radians”, that is a unit of measurement of an angle and a distance along an angle;
D) the target is changed (who or what could be?).
2. The solution contains references to the classic method for navigation with a map and a compass.
Zodiac provides the azimuth, i.e. the angle in degrees between magnetic north and the imaginary line to follow to reach the target, which is the distance as the crow flies from the top of Mt. Diablo to the place where the bomb is.
This explains why he asks to combine the code and the map (A) and to set the arrow on the map towards magnetic north (the arrow is a compass needle) (B).
3. After turning the compass needle towards magnetic north and completing the rotation, the “final” arrow made up of the aligned segments of the compass will precisely point the area indicated in the solution of the cipher.
4. In the plaintext there are the measurements of an angle and a distance. They are expressed in degrees, the standard measurement for navigating with a compass, and in miles.
The distance of 14 miles (consisting of the “final” arrow on the map) “along” the 570° degree of the azimuth explains the meaning of the last part of Zodiac’s tip “…# inches along radians” (C).
5. Both the size of the angle and the distance are not random.
The distance is given by Zodiac since it is the sum of the segments dividing the quadrants of his compass. The “final” arrow, in fact, represents on the map the distance on the map between the Mt. Diablo peak and the place where Zodiac set the bomb.
6. Half of the numbers of which the distance is composed of as well as 2/3 of the numbers of the angle are replaced by letters of the Latin alphabet and have been transposed according to the following reverse alphabetical order W → N = 0 → 9.
7. The possible target of the bomb is much compatible with Zodiac’s attitude emerging in his letters and the other ciphers (D).
In the area indicated by the decryption, there is a building used by the Alameda County Sheriff’s forces, known at the time for clashes with Berkley protesters, who nicknamed them “blue meanies” (the enemies of the Beatles in the movie “Yellow Submarine”), as reported by the New York Times and it is confirmed by a sign at the Alameda County Sheriff’archive.
In the previous letter postmarked “April 20, 1970”, Zodiac associated the term “blue meannie” (sic) with a policeman killed by a bomb.
The building is called “Eden Township”. The Garden of Eden is the “terrestrial paradise”. “Paradice” is a recurring and emblematic word in the Zodiac case, as well as the key to solve the final anagram in the Z408, according to the solution I proposed here.
8. There are two replacements in common with each of the other Zodiac texts encrypted with substitution ciphers:
– the Z408 solved by the Hardens in ’69;
– the Z340 deciphered by David Oranchak, Jarl Van Eycke and Sam Blake in December 2020.
I have reported all the replacements in the image below.
Zodiac, il Mostro 
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