The contention is that Zodiac created his own code key, as seen here.
Accompanying the Button Letter 32 Symbol code was the Phillips 66 Road Map with the Zodiac crosshair centered over Mount Diablo. 'The conventional view is that the peak derives its name from the 1805 escape of several Chupcan Native Americans from the Spanish in a nearby willow thicket. The natives seemed to disappear, and the Spanish soldiers thus gave the area the name "Monte del Diablo", meaning "thicket of the devil." Monte was later misinterpreted by English speakers as mount or mountain." Taken from Wikipedia. The number of the beast is 666.
To save time I will add in here a previous article before continuing.
The Zodiac Killer mailed us the Button Letter and Phillips 66 Petroleum Map on June 26th 1970 stating "The Map coupled with this code will tell you where the bomb is set. You have until next fall to dig it up." Then one month later he mailed the Little List Letter on July 26th 1970, giving us a further cross-haired diagram and the phrase "PS. The Mt. Diablo Code concerns Radians & # inches along the radians." This was basically a further clue to push us in the right direction.
The first thing to look at is the Phillips 66 Map crosshair with numbers around its cardinal points, the number 0 facing north, the number 3 on the east axis, the number 6 on the south axis and finally the number 9 on the west axis. It is easy to consider these as clock points, however the number 12 is replaced by a zero, so we will refrain from doing so. But what relevance do these numbers have, bearing in mind we are looking for a grid position on where the bomb is set and considering a clock face does not begin on zero. The Zodiac mentioned 'radians and inches along the radians,' we know a radian to be valued at 57.296 degrees, so all we have to do is travel around the circumference of his crosshair situated over Mt Diablo, by a fixed number of radians. Then once we have found the correct amount of radians, we travel away from that point, along the radian in inches, until we locate the bomb. But how many inches. The only numbers we have are the ones Zodiac placed around the crosshair, and these are situated along the radian line, so these are what we'll use to formulate the answer.
We have 8.2 inches, so with a simple calculation we multiply 8.2 by 6.4, to give us our distance to travel away from Mount Diablo.
8.2 X 6.4 =52.48 miles. In other words the bomb is set 52.48 miles from Mount Diablo at an angle of 246 degrees. But bear in mind the Zodiac stated "The Map coupled with this code will tell you where the bomb is set. You have until next fall to dig it up."
So the code of 32 symbols has to tie in with this location.
Below is a diagram with an angle of 246 degrees radiating from from Mount Diablo, you will notice it passes over the bold circle Zodiac drew and lands in the area of San Francisco International Airport. In fact it is virtually 52.48 miles on Google Maps to this location. Here is the area of South Linden Avenue, right next to San Francisco International Airport, shown as being 52.90 miles from Mount Diablo.
The relationship between the characters in the 32 Symbol Cipher and San Francisco International Airport do not appear to throw up any correlation, even with the three repeating symbols, if of course the airport has any relevance whatsoever. Using the magnetic north value of 17 degrees in 1970 it was discovered that this location is set at 4 radians or 229 degrees. In other words one radian of 57.296 degrees was multiplied by a factor of 4.
The numerical value of 888 has also been discovered in the 13 Hole Postcard using this method, along with far simpler mathematical techniques on the Pines Card and Halloween Card.
He gave us a four in 4-TEEN, but regardless of this, multiplied by a factor of 4 gives us 888 once again. To expand on the subject of mathematics in the Halloween Card click here.
There is other little known potential Zodiac correspondence, described in the FBI files here, called the 'FLT 555 Cancer Card.' The correspondence was mailed on December 10th/11th 1969 and is actually two paste up pages entitled 'DAY BY DAY FORECAST FOR CANCER' and 'DAY BY DAY FORECAST FOR LEO', with multiple notations including 'FLT 555' and 'FLT THREE OF A KIND VVV'. Many people have interpreted this as flight 555, however it is curious that he again gives us a factor of 111 and actually highlights 'three of a kind'. In fact the three V's could be interpreted as Roman numerals for five, but equally, if we look at our gematric code key above, three V's would be represented as 555.
The 408 was a rudimentary substitution cipher, which he followed up with three 'uncrackable' codes, however it may turn out that these codes were more basic than his first. We may just be looking in the wrong direction to unearth his simple mosaic of mathematics.