The following will examine some small features of the opening two lines of the cipher, exploring the idea that the Zodiac employed some form of 'pigpen cipher' where geometric shapes are substituted for alphabetical characters.
Below are two examples which simplistically demonstrate this concept- the first of which assumes he opened up his 340 cipher with his usual introduction "This is the Zodiac speaking." The second using the opening three letters of the cipher and turning it into familiar wording in respect to the Zodiac murders.
It may be typical Zodiac humor. We shall then apply "This is the Zodiac speaking" to the first and second lines of the cipher, applying "I have killed" as the follow up, reminiscent of his opening phrase in the 'Bus Bomb' letter, where he stated "This is the Zodiac speaking up to the end of Oct I have killed 7 people."
The word "shit" in both diagrams is spelled out clockwise. The red circled 'V' characters on the right marry up with the two diagrams above. The blue circled character does not- unless of course after a set number of deciphered characters the key is rotated. Diagram 1 would have to be rotated 90 degrees anticlockwise, whereas Diagram 2 would have to be rotated 45 degrees anticlockwise, so that the 'I' in Zodiac now matches the key again.
If we take the 340 cipher and the April 20th 1970 '13 Symbol' cipher as somehow connected, then by adding the opening three alphabetical characters of the 340 cipher to the last three alphabetical characters of the '13 Symbol' cipher (in reverse), the name 'HERMAN' is created. By adding the last alphabetical character of the 340 cipher to the first three alphabetical characters of the '13 Symbol' cipher, we create an anagram of 'KANE'. This can also be achieved using the first four alphabetical characters of the '13 Symbol' cipher. This really doesn't mean much or get us anywhere, but it just leads us to our second example of the type of key Zodiac could have used. The next diagram (below) shows the 'V' symbols arranged around a circle- the two red circled symbols are two the Zodiac never used in the 340 cipher and can be disregarded.
Let us now take 'Herman' and extend it to 'Herman Road' something we are familiar with, and place it at the beginning of the 340 cipher.
The letters M, N, R and O in 'Herman Road' match the clockwise alphabetical key on the left. It can be noted that the key fails after four 'V' symbols, as in the above example. So once again the key would rotate forwards or backwards. To be specific- the 'V' symbols would switch places through 135 degrees clockwise, or possibly anticlockwise. Then 'murders' incorporates the new key.
Had the Zodiac employed something similar, there is no limit to his creativity, or the number of key rotations he could employ. Additionally, different key configurations can be created for the same alphabetical letter, making it even harder.
The images at the top of the Wikipedia page show how this approach can be adapted to any number of configurations. The four dots shown in the 'pigpen cipher' examples, remind us of the 'Halloween' card configuration. But whether this was some form of key or clue has yet to be fully established. The two examples presented above are undoubtedly incorrect, however, they serve the purpose of showing how devilishly creative the Zodiac could have become when he concealed his message on November 8th 1969.