He then released his 'masterpiece' upon the world, the 340 cipher on November 8th 1969, again on the first day of the week on the 13 moon calendar, with the 'Dripping Pen' he used to signify his list was underway.
After the Bus Bomb Letter he mailed yet a further segment of Paul Stine's shirt to prominent attorney Melvin Belli on December 20th, exactly one year to the day of his first entry, that of the Lake Herman Road double murder of David Faraday and Betty Lou Jensen, this again fell on the first day of the 28 day month,13 cycle calendar.
Following this, two months later was the John Hood and Sandra Garcia killings on a remote beach in Santa Barbara on February 21st 1970, yet again the first day of the week in the 13 moon calendar.
The Zodiac then mailed his 'My name is cipher' reminding us with exactly 13 symbols.
Four and one half months later a crime not usually associated with the Zodiac Killer, the Sleeping Bag Murders of Thomas Dolan and Homer Shadwick on a beach in Santa Barbara sometime on the night of July 4th 1970, exactly one year to the day of the Blue Rock Springs attack on Michael Mageau and Darlene Ferrin, once more fell on the first day of a 13 moon calendar.
The disappearance of Judith Hakari on March 7th 1970, with her eventual discovery and the murder of Nancy Benallack on October 25th 1970, both in Sacramento, were two additional dates to have relevance to his list on the calendar.
Then came his biggest clue to date, obviously tired by the apparent inability of the authorities to see his cunning masterstroke, he tabled a little list for us all with the strongest hint yet based on the number 13.
The Little List Letter was mailed on July 26th 1970, the first day of the week on the 13 moon calendar and displayed a large crossed circle emphasizing the number 13, to indicate why this particular number has relevance to his crimes and incidentally the date, July 26th, marks the beginning of the astrological 13 moon calendar year, unlike the Gregorian Calendar that begins on January 1st.
After the crosshair symbol he begins on his little list, taken from the Mikado 'As some day it may happen' and on the 13th line of his writing he drops a hint 'are up in dates' , imploring us to see that the answer to his crimes are solely driven by particular dates and further reminders are yet to come.
By the time of the Little List Letter claiming 13 slaves, 11 of the already mentioned victims above had fallen on the first day of the week on the 13 month calendar, leaving two unaccounted for, although by the time of the 13 Hole Postcard that figure would reach 12.
Just over a month later Donna Lass disappeared after finishing her shift at the Sahara Tahoe Hotel on September 6th 1970, you've guessed it, the first day of the week on the 13 moon calendar.
Then came the 13 Hole Postcard, one month after Donna Lass's disappearance, a card laden with 13 punch holes (13 moons) and part of the text, not content with just the number 13, made a play by stating 'The pace isn't any slower,in fact its just one big 13th'. Bearing in mind this correspondence was the one immediately after the Little List Letter, was he reminding us about the 13th line and his murders being 'Up in dates' , after all his ego wanted us to applaud his cunning without actually telling us directly.
Next up was the Halloween Card and what could be taken as 13 eyes or 13 crescent moons, but 13 nonetheless, and a 7F symbol.
7F ( F being 6 ) could produce 13 and the 4 dots linked to the 4-TEEN writing on the card referencing the fact that four of his victims were teenagers.
The following letter was the Los Angeles Letter mailed on the 13th March 1971.
The Pines Card was was then received on March 22nd 1971 and Harvey Hines, a retired law officer believed the punch hole in the top right corner to be a possible burial site or significant area. In 1976 Otto Fredericks out hiking for the day discovered a crucifix of supposedly 13 stones, remember the 13 Hole Postcard portrayed a crucifix and the number 13 and the Halloween Card depicted the words PARADICE and SLAVES in the form of a crucifix with the sum total of letters adding up to 13.
Only the Exorcist Letter was given much credence after this and was widely believed to be Zodiac's final act.
When he stated ME -37 SFPD - 0, was he giving us the final date in the jigsaw, his birhdate of ME - 3/7 , the 7th March, which incidentally falls nicely on the first day of the 13 moon calendar for one final time, if indeed it was his last correspondence, before the Zodiac Killer tired of his 'fun and games', retired into anonymity for good.
However the SLA Letter backing this letter up was sent on February 14th 1974 and whether or not it was genuine material penned by the killer, it too landed on the first day of the 13 cycle calendar.
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