On July 13th 1971, the Zodiac Killer claimed his involvement in the April 11th 1971 murder of Kathy Bilek, brutality stabbed at Villa Montalvo in Saratoga. The Monticello card also inferred his involvement in the murders of Kathy Snoozy and Deborah Furlong on August 3rd 1969 in San Jose. This wasn't the first time he implicated himself in the murder of these girls, and it wouldn't be the last. On April 29th 1971, Karl Francis Werner (18) was arrested for the knife slayings of all three girls, much to the surprise of many who knew him. Karl Werner, a lanky 6'2" freshman at San .lose City College, who worked six nights a week at a hamburger stand, was described by his boss as “very sincere, hard-working, quiet, of good character.” Eve Schulman, 19, a classmate who rode to the campus with Werner each day, called him “the typical boy next door.” She said Werner, a high ranking student in mathematics and physics, who has been constructing a computer as a class project, is “really smart, really neat.”  

I believe the Zodiac Killer constantly followed the newspapers with respect to the murders he was claiming. He knew that if the police believed he was the likely murderer his reign of terror would be continue, and the newspaper coverage he so badly craved would extend his perceived legacy. The newspaper cutting on the left was authored by Paul Avery (a journalist from the San Francisco Chronicle), and somebody the Zodiac Killer followed closely at the height of his 'reign of terror'. Karl Francis Werner had just been arrested for the murders of the three young girls, and his story was covered by Paul Avery on April 30th 1971 under the title of 'San Jose Student Held in Slaying of Three Girls'. In a revised timeline, I believe the Zodiac Killer responded to this particular newspaper article, when he mailed the '148 Character' cipher to the San Francisco Chronicle, most likely in the May of 1971. 

The newspaper article stated "He was immediately advised of his rights concerning any statements he may make and legal representation to which he is entitled, the detectives said. Werner was then taken to the scenes of the crimes. Late yesterday her was undergoing questioning. The detectives would not reveal what statements, if any, he had made concerning the killings of the three girls". The Zodiac Killer would respond in his decoded letter to the San Francisco Chronicle, warning the police "Tis the Zodiac Speacking. Why can't you stop me. I can't stop killing. Stop listening t(o) phonys. If this is not on your front page in a week I will skin 3 little kids and make a suit from the skin" (coded section).  

He was effectively saying to police who were questioning Karl Werner "stop listening to this phony (impostor, fraud). I am the real killer". In view of the title of this article 'San Jose Student Held in Slaying of Three Girls', it probably isn't too surprising he threatened a further "three little kids" if they didn't print this letter and cipher on their front page. 

He also wrote on the '148 Character' cipher letter "Next time I will send a patch of skin if their is some left over". Bearing in mind the 200+ stab wounds these young girls suffered, this statement doesn't require much explanation. 

Both the Monticello card and '148 Character' cipher inferred a total of 21 victims, suggesting they were authored by the same individual.    

Sometime in 1971 a questionable Zodiac correspondence and cipher was received by the San Francisco Chronicle, postmarked Fairfield, California. This was now the fourth Zodiac related communication mailed from Fairfield, following the December 7th, December 11th and December 16th 1969 trinity. There is limited widespread information regarding this letter available on the internet other than the Zodiologists.com website, who have analyzed this correspondence in great detail. The letter and cipher is to be found using the Wayback Machine on Ed Neil's old website TheZodiacFiles.com. I have cleaned up the letter without altering any of the text by the author:

I'll DO IT TO BECAUSE I DONE IT 21 TIMES. I CAN'T STOP BECAUSE EACH ThAT I KILL MAKES IT WORSE AND I MUST KILL MORE. MAN IS ThE MOST PRIZED GAME. ILL NERVER GIVE MY NAME BECAUSE YOU dONT UNDERSTAND. NEXT TIME I WILL SEND A PATCH OF HUMAN SKIN if their is SOME Left OVER.

The 148 character cipher decodes to:
"Tis the Zodiac Speacking. Why can't you stop me. I can't stop killing. Stop listening t(o) phonys. If this is not on your front page in a week I will skin 3 little kids and make a suit from the skin". 
The wording in the letter "I'll do it to because I done it 21 times" is consistent with a mailing date sometime after the March 13th 1971 'Los Angeles' correspondence from Zodiac, claiming 17+ victims. Using a simple calculation we can estimate how often the Zodiac claimed a victim. From December 20th 1968 to July 26th 1970 Zodiac claimed 13 victims over 584 days. That is one victim every 44.9 days. Therefore, from victim 13 to 21, another 8 victims were claimed (8 X 44.9 = 359 days). Add 359 days to July 26th 1970 and we arrive at July 20th 1971, approximately four months after the 'Los Angeles' letter.

This letter and cipher appears at first glance a dubious Zodiac communication, but as Zodiologists.com point out, how difficult would it be for a hoaxer to mimic the ciphers or crosshairs of Zodiac. The fact the author failed to do this, should be pause for thought. There is also something about this letter that indicates the author had written another 'Zodiac' communication (or the author was the actual Bay Area murderer). The other communication, also mailed to the San Francisco Chronicle on July 13th 1971, mirrored the 148 character cipher and letter in one crucial way - the victim total. The last two widely accepted Zodiac communications were the March 13th 1971 'Los Angeles' letter claiming 17+ victims, and the January 29th 1974 Exorcist letter  claiming 37 victims. The author of the above correspondence had 19 victim totals to choose from (18 to 36), yet he chose 21, the exact total mentioned in the July 13th 1971 'Monticello' card, which featured in the San Francisco Police Department DNA report under "suspected Zodiac correspondence". Did the author of the above correspondence just get lucky, in accidentally choosing 21 victims like the 'Monticello' card, or was he the author of both?

The 'Monticello' card was mailed on July 13th 1971 stating: 
'Near Monticello Shought Victims 21 ...... In The Woods Dies April'.
By my rudimentary calculations the 148 character cipher and letter should have been mailed on July 20th 1971, only one week after the 'Monticello' card. If somebody can find the exact date of mailing regarding the 148 cipher and letter, or when this correspondence was published in the San Francisco Chronicle, it would be of immense value. The 'Monticello' card, by all accounts, was not published in the newspapers. If this were the case, then the victim total of 21, chosen by two independent authors looks extremely unlikely. If the 'Monticello' card was designated as "suspected Zodiac correspondence" by the San Francisco Police Department, then by extension, the above correspondence should be afforded the same value.        

Denise Kathleen Anderson (22), who resided in Sacramento, was last seen on April 13th 1971 by her roommates at approximately 05.30 am - and as of writing her disappearance still remains a mystery - although foul play is suspected. What occurred with Denise Kathleen Anderson after last being seen by her roommates is unknown, but her disappearance (and possible murder) again took place in Sacramento, near Interstate 80, only five months after the murder of Carol Beth Hilburn and exactly one month after the Zodiac 'Los Angeles' letter mailed on March 13th 1971, claiming 17+ victims. In this correspondence Zodiac stated "If the Blue Meannies are evere going to catch me, they had best get off their fat asses + do something. Because the longer they fiddle + fart around, the more slaves I will collect for my after life." The question is, was Denise Kathleen Anderson one of them?
She disappeared on April 13th 1971, so the 'Monticello' card (with break added) could be referring to the possible murder of Denise Kathleen Anderson in the woods during April:
'Near Monticello Shought Victims 21 ...... In The Woods.  Dies April'.
The 148 character cipher and letter stating "I'll do it to because I done it 21 times" could very well be confirmation that the victim he sought (possibly Denise Kathleen Anderson) had now been claimed.

What are the chances the 'Monticello' card was also mailed from Fairfield? Denise Kathleen Anderson lived in Sacramento,  only 43 miles from Fairfield - but was she the 21st victim of the Zodiac Killer?