As explained in the previous article, there appears little doubt that the author of the "concerned citizen" card had read the August 9th 1969 San Francisco Chronicle article entitled 'A Murder Code is Broken'. The article clearly stated that Donald Harden's worksheets had been forwarded from the Chronicle to the Vallejo Police Department (which would obviously contain the cipher key and method of decryption). It stated "Vallejo Police Sergeant John Lynch, in charge of the investigation of the murders and of the cipher letter writer, asked The Chronicle to send Harden's code breaking worksheets to him for further checking; which was done." The wording "cipher letter writer" is an unusual combination of words, that apparently didn't go unnoticed by the "concerned citizen" author, who used the same sequence in his opening gambit: "I hope the enclosed "key" will prove to be beneficial to you in connection with the cipher letter writer."  
This should be proof enough that the "concerned citizen" had read the Chronicle article, knew the code had been broken, and knew Donald Harden's worksheets had already been sent to the Vallejo Police Department and Sergeant John Lynch. Therefore, do you have to question the integrity of the "concerned citizen" regarding the motivation behind his August 10th 1969 mailing?    

​The Vallejo Times-Herald also broke the story on August 9th 1969, stating "Lynch talked to Harden and said, "I'm convinced he has it solved". He said he would talk to him again today. Meanwhile Lynch has Harden's worksheets and is studying and comparing them with the three-part cryptogram and the translation." 

So, having presumably read all this, was the "concerned citizen" just a helpful member of the public attempting to corroborate the Harden's solution, or did the Zodiac Killer, knowing his cipher had been broken quickly, begin playing a game of 'cat and mouse'. The author of the "concerned citizen" card didn't want to give the Vallejo Police Department his name for fear it would be published in the newspapers, just like Zodiac stated in the 408 - but did the anonymous card reveal his identity? 

The "concerned citizen" card only contained 69 words, so why did the sender bother to type the message rather than write a handwritten message or simply capitalize the text.
When he wrote the cipher key he capitalized the alphabetical letters to mirror the 408, so what purpose was behind him choosing not to do this in his message?

The sender would certainly not have given away his identity by using upper case lettering in the message (as he had already done it in the key), nevertheless, he chose to type it anyway. If the author was the Zodiac Killer, did he believe, that by using capitals in his message rather than handwriting it may have been construed as suspicious, so opted to use a typewriter for a more professional approach and give the card a level of credibility. Opting to write the message in his normal handwriting would obviously have given the game away. He also may have thought it easier to type the message rather than make the effort to disguise his handwriting. The cipher key was obviously written rather than typed because of the unusual characters present within the 408 cipher not being available on a standard typewriter. 

This is all very speculative, however, with very little to indicate one way or another as to the identity of the "concerned citizen", feeding on scraps may be the only avenue. Was the sender of the August 10th correspondence simply being a helpful citizen wanting to corroborate the Harden's solution, or Zodiac attempting to regain a semblance of lost pride by surreptitiously offering a lending hand to the Vallejo Police Department, declaring "I do not wish to have my name in the papers".
This may have been the Zodiac Killer's idea of a joke, after having previously stated "I want you to print this cipher on the front page of your paper. In this cipher is my idenity."
This contradiction certainly wouldn't have been lost on a killer who craved attention at every turn.
A killer who was prepared to confuse with "name" and "identity" in his first communications with the newspapers, would not be averse to creating similar parallels with "signature" or "name" in the "concerned citizen" card just ten days later. 

THE CONCERNED CITIZEN CARD [PT1]

Having not covered this topic previously, I thought I would add the "Concerned Citizen' card to this site, mailed from San Francisco and postmarked August 10th 1969, one day after the article 'A Murder Code is Broken' featured in the San Francisco Chronicle newspaper. In this article "Vallejo Police Sergeant John Lynch, in charge of the investigation of the murders and of the cipher letter writer, asked The Chronicle to send Harden's code breaking worksheets to him for further checking; which was done." (see foot of article for newspaper cutting).     

Many have asked the identity of the "concerned citizen."  Was it Donald Harden, the Zodiac Killer or a third party who broke the code independently? The latter having not been aware of the code being broken, as published in the newspaper.
The Chronicle, according to the August 9th 1969 newspaper article had "already done" sending Sergeant John Lynch the worksheets, so why would Donald Harden be mailing the cipher key through the mail, when clearly he was already in contact with police. Therefore, this option can be summarily dismissed as the least likely option. 

The Bay Area murderer, as of August 4th 1969, had already given us his pseudonym with the dramatic introduction of "This is the Zodiac Speaking", so why would he now be acting coy in giving us the cipher key under the guise of a "concerned citizen". This tactic may have surfaced during the 1974 communications, but to implement it so early, just after threatening to "cruse around all weekend killing lone people in the night then move on to kill again, until I end up with a dozen people over the weekend", seemed an immediate backpedal. From "ruthless killer" to "concerned citizen" in a matter of days.
On the other hand, this may have been the start of his game with both the newspapers and law enforcement alike. 

The card reads:
Dear Sergeant Lynch.
   I hope the enclosed "key" will prove to be beneficial to you in connection with the cipher letter writer.
  Working puzzles criptograms and word puzzles is one of my pleasures. Please forgive the absence of my signature or name as I do not wish to have my name in the papers and it could be mentiond by a slip of the tongue.
      With best wishes.
                                     concerned citizen.

Although it has been stated on many forums that the author of the "concerned citizen" card may have mailed it, unaware of the code being broken and published in the San Francisco Chronicle on August 9th 1969, this seems highly unlikely. The author used the wording "cipher letter writer", exactly as published in the newspaper. This, from a grammatical standpoint, is highly likely to have been copied from the newspaper, indicating that the person who mailed in the cipher key already knew it had been broken. This could indicate it was Zodiac after all.

Zodiac researcher David Oranchak has comprehensively covered all aspects of the Zodiac ciphers on his excellent ZodiacKillerCiphers website, including two articles on the topic covered in this article. The first is a 'Detailed Analysis of the 408 Solution'  and the second is entitled 'Who is the Concerned Citizen'. The latter will show you the code key mailed by the "concerned citizen" for handwriting comparison purposes. 
​
THE CONCERNED CITIZEN CARD [PT2]

Vallejo Times-Herald - Cryptogram Deciphered by Teacher August 9th 1969