His key was developed by splitting of the alphabet, A through to M and N through to Z. We can see that the '13 Symbol' cipher begins with an A and ends with an M. So, what we will do first, is place the alphabet alongside the '13 Symbol' cipher and see if we can find any organization or patterns that exist using simple mathematics.
The 340 cipher was the Zodiac Killer's unsolved masterpiece, and being a man with an inflated ego, driven by self publicity, what better way to drop us a hint by placing his signature or pseudonym on the final line of the 340 cipher. You will notice he placed the Zodiac crosshairs symbol, followed by what could be interpreted as Zodiac, and then an upside down Aries symbol (with a line on the top and a dot to the left). So, what we shall do is place the correct spelling of Zodiac alongside the version he placed on the 20th line of the 340 cipher and use the identical technique we used to create the symmetry on the '13 Symbol' cipher. The alphabetical difference of ZOD produces three zero's, the IAC produces 888. These two sets of figures meshed together gives us the three circled 8's found on his next cipher, as though he was carrying them forward. It is also apparent on the '13 Symbol' cipher, that either side of the three circled 8's are the Zodiac crosshairs and an inverted Aries symbol, almost identical to the final line of the 340 cipher. So, the author has effectively carried eight symbols from one cipher to another.
Previously, it was shown that the Zodiac crosshairs were attributed a value by the Zodiac Killer, using a code directly obtained from the '13 Symbol' cipher. It can be seen below, that like the '13 Symbol' cipher, it is based on a split alphabet, however, what it reveals takes the mathematics of the '13 Symbol' cipher to a whole new level.
Even the name KANE or CANE, heavily attached to the Donna Lass case by detective Harvey Hines, produces the numbers 3,1,1,5 in the code (315 in order). Also, if we attribute the gematric value to the letters in the '13 Symbol' cipher it produces 1,5,1,3,1,1,1 and 1, generating the same three numbers once again. So one can see, either attributing gematric values or numerically counting the alphabetical difference on the '13 Symbol' cipher, only the whole numbers of 3,1 and 5 are ever produced. See 'The Hidden Message in the Pines'.
Since the Zodiac was created using the horoscope, it was only fair to consider the '13 Symbol' cipher from the standpoint of Zodiac signs, in that the circled 8's may have been circled for a dual purpose and could be interpreted as three Taurus signs.
In the 'Peek Through the Pines' article we did just that, and placed all these values into the gematric code.
The crosshairs were 315, 3 X TAURUS = 93, ARIES = 22, and the remaining alphabetical letters A,E,N,K,M,N,A,M = 14. The total was 444, exactly half of 888. However, both numbers are well known to religion. 888 is the figure representative of Jesus or Christ the Redeemer in Christian numerology and 444 is representative of Jesus in standard English gematria. But no matter which way you interpret the '13 Symbol' cipher, either as three 8's or three Taurus symbols, the end result is religion.
The figure 444 was then found in the 'Button' letter code (see article above), and the figure 888 was found in the '13 Hole' postcard, 'Halloween' card and 'Pines' card, bringing us full circle. Even the 'Bus Bomb' letter overlay, mailed one day after the 340 Cipher, was aligned over his four crimes at Lake Herman Road, Blue Rock Springs, Lake Berryessa and Presidio Heights. But more crucially, his first three murders of David Faraday, Betty Lou Jensen and Darlene Ferrin all fell over the 8 o' clock position on the overlay, giving us 888 once again. SEE HERE.
The Romans did not number days of a month sequentially from the first through the last day. Instead, they counted back from three fixed points of the month: the Nones (5th or 7th, depending on the length of the month), the Ides (13th or 15th), and the Kalends (1st) of the following month. The Ides occurred near the midpoint, on the 13th for most months, but on the 15th for March, May, July, and October. The Ides were supposed to be determined by the full moon, reflecting the lunar origin of the Roman calendar. On the earliest calendar, the Ides of March would have been the first full moon of the new year. Taken from Wikipedia.
The Ides of each month occurred on the 13th and 15th, the numbers 3,1 and 5 once again and strangely the IDES OF MARCH in the gematric code = 5+4+5+6+2+6+1+1+5+3+6 = 44, the exact date of Julius Caesar's murder. But is mathematics the enemy here, or quite possibly a bright new dawn.