Vallejo Times-Herald: "Here is a cyipher or that is part of one. the other 2 parts have been mailed to the S.F. Examiner + the S.F. Chronicle."
San Francisco Examiner: "Here is a cipher or that is part of one. The other 2 parts are being mailed to the Vallejo Times + S.F. Chronicle."
San Francisco Chronicle: "Here is part of a cipher the other 2 parts of this cipher are being mailed to the editors of the Vallejo Times and SF Examiner."
You will notice the two San Francisco newspapers are being addressed in the present tense regarding the other two mailings, using the word ARE. While the Vallejo Times-Herald newspaper is being addressed in the past tense regarding the other two mailings, using the word HAVE. There is every indication that this has been written subconsciously by the Zodiac Killer and therefore he has inadvertently given us his home location of Vallejo. The word "are" immediately precedes Vallejo Times on both occasions.
In two of the communications to the Chronicle and Examiner in San Francisco, he is referring back to his hometown Vallejo in conjunction with another mailing. Therefore he uses the plural form of the present tense, in the word "are". That is because at this moment in time (the time of writing), he is present here in Vallejo, so is effectively forced to abandon the past tense of "have". The Zodiac Killer cannot refer to Vallejo in the past tense in this instance, because the Vallejo Times-Herald office is in his locality, and therefore he is referring to it in the present of "are".
Anything in the Zodiac Killer's locality is the 'here and now.' Anyplace one has to travel and return, whether in the mind or reality, will be referred to in the past tense. Traveling to San Francisco physically and returning to Vallejo will now be referred to as "I have mailed", because of the distance you associate with the offices of the San Francisco Chronicle and San Francisco Examiner from Vallejo. Even if you do it in your mind. But the Vallejo Times-Herald office is effectively on your doorstep and will therefore be seen as in the "here and now" to somebody living in Vallejo, without any real distance associated with it. Therefore, it doesn't need to be referred to in the past tense, which is exactly what Zodiac does in two of his communications regarding the mailing to Vallejo- he uses the word "are".
Zodiac is in his house opposite the Vallejo Times-Herald office and he has just finished preparing his three July 31st 1969 letters for delivery. He bids farewell to his housemate and travels to San Francisco to post his letters. Upon his return two hours later he says to his friend "I have posted two letters to the San Francisco newspapers". Looking out of his window and pointing he states "One letter is being posted to the Vallejo Times-Herald." He would be using the present tense regarding something in the "here and now". But because he is referring to the Vallejo Times-Herald mailing in two communications he uses the present tense "are". It clearly indicates that on a subconscious level the Zodiac Killer is referring to Vallejo in the present tense, because that is where he was when he penned the three July 31st 1969 letters.
The old Vallejo Times-Herald office was at 440 Curtola Parkway, just 0.96 miles (as the crow flies) from the Springs and Tuolumne payphone.