'For 35 years starting in 1965, the San Francisco Chronicle and Examiner operated under a Joint Operating Agreement whereby the Chronicle published a morning paper and the Examiner published in the afternoon. The Examiner published the Sunday paper's news sections and glossy magazine, and the Chronicle contributed the features.' Wikipedia.
The first newspaper article was released by the San Francisco Chronicle on Saturday August 2nd 1969. Jack E Stiltz requested the writer to send a second letter "with more facts to prove it." The second newspaper article followed on Sunday August 3rd 1969 in the San Francisco Examiner. Jack E Stiltz was 'still not convinced the letters and codes were written by the actual killer.' The police chief 'urged the writer to send more letters, with more facts to prove his connections to the crimes.' The 'Debut of Zodiac' letter was received by the San Francisco Examiner the following day, so it is likely he is responding to the Sunday article in particular. This may be important if we analyze the nature of the communication and the actual paper it is written on.
This may have come into play when the Zodiac sent his August 4th 1969 letter. The Zodiac had just embarked on his letter writing campaign, when he mailed the 408 cipher on July 31st 1969, split into three sections of 136 characters, each mailed to three newspapers, the San Francisco Chronicle, San Francisco Examiner and Vallejo Times-Herald, all of which decided to publish. When Jack E Stiltz questioned the validity of the letter writer, Zodiac was eager to reply, shown by the very fact his response was received on Monday, the day after the August 3rd 1969 Sunday Examiner article. He must have hurriedly drafted a response in order that his letter was published in the Monday edition, but with one key difference.
The Zodiac Killer used Eaton brand paper in his communications with the newspapers, but the 'Debut of Zodiac' was a notable change using Woolworth's Fifth Avenue paper, as though he was thrown out of his routine. No doubt he kept a supply of Eaton paper at his residence, which he reverted back to after the 'Debut of Zodiac' letter. It seems like the Woolworth's Fifth Avenue brand paper was a rushed buy, when he had no easy access to his home location, yet was still in a location to readily purchase the Sunday Examiner newspaper.
Here is one possible scenario, but obviously not the only one.
'The Zodiac Killer has just completed his 408 cipher and the weekend is approaching. He decides to use his Saturday and Sunday off work to relax and bask in his new found notoriety. If he is a resident of Vallejo or Benicia, then a thirty mile weekend trip away to San Francisco, may seem like a justified reward to enjoy his passion of theater in the Union Square and Tenderloin District. San Francisco may be an area he is already familiar with, if he works there. Then Jack E Stiltz puts a fly in the ointment by issuing a doubt that the killer and letter writer is the same person. The Zodiac Killer enjoying a cup of coffee over breakfast in his hotel getaway, picks up his paper and nearly chokes when he reads the article. Young and impulsive, his need to respond is immediate before Monday's edition. He finishes breakfast in his theater district hotel and heads to the nearest stationers to purchase some paper and a felt tip pen.' Enter Robert Graysmith.
His Eaton paper was at his residence, but he is on a weekend trip. The easy option is to purchase a temporary pad of paper from the nearest location and Woolworth's would have been the obvious choice. It is in the heart of the theater district, just 10 minutes walking distance from Union Square and the Westin St Francis Hotel, the location where Zodiac was believed to have flagged down Paul Stine just two months later on October 11th 1969.
Robert Graysmith highlights the Westin St Francis Hotel at Union Square, along with the Pinecrest Restaurant in his book 'Zodiac', whereas the article in the San Francisco Examiner on October 23rd 1969 stated "The search also took police to Nob Hill, where the Fairmont Hotel became involved again in the manhunt. This was because: Cabbie Paul Stine, 29, the Zodiac's latest victim is believed to have picked up his fare on a street near the famed hotel. A waitress in the hotel candy shop-fountain told police she served coffee during the television show (Jim Dunbar/Melvin Belli) to a man who resembled composite drawings of Zodiac. She saved the cup and saucer for a fingerprint check."
Ironically Zodiac, if a visitor at one of these hotels, would add a footnote to his 'Debut of Zodiac' letter declaring "No address".
The Zodiac Killer would later send two further missives, the 'Little List' and 'Exorcist' letter, in which he featured the Gilbert and Sullivan satirical comedy, The Mikado, which played in the San Francisco theater district during this period. This location of Woolworth's, the theater district, the offices of the San Francisco Chronicle and San Francisco Examiner and the pick up point of Paul Stine on October 11th 1969, certainly center the focus on this small area of San Francisco. The San Francisco Chronicle at 901 Mission Street/corner of 5th and San Francisco Examiner at 835 Market Street are key locations.
However this murder was a little different. If the killer, as suggested earlier was not a resident of San Francisco, but a guest at a hotel somewhere in the theater district, then you would assume this murder was pre-planned, with a vehicle or three mile walk back to Union Square.
Just like the 'Debut of Zodiac' letter that was received at the San Francisco Examiner on the immediate Monday to the article, so was the Paul Stine letter, containing the swatch of the taxicab driver's shirt, on October 13th 1969. His response to both events was immediate, yet this time, knowing his murderous intentions, was prepared with pen and paper in advance.
If the Zodiac Killer was a regular visitor to the area of San Francisco's theater district, the Northpoint Theatre, easily accessible from Union Square, likely saw the murderer through its doors at some point, although he appeared notably underwhelmed, describing it as "the best satirical comedy that I have ever seen,"
Does the change in writing material give us an insight into the Zodiac Killer's movements precedent to the 'Debut of Zodiac' letter, or is it simply a case of reading nothing into something.