The author attached a drawing of blood dripping from a knife, entitled "The Bleeding Knife of Zodiac". Zodiac had previously claimed seven victims in the Bus Bomb letter mailed to the San Francisco Chronicle on November 9th 1969, so it wasn't surprising to see this knife drawing had 7 drops of blood falling from the blade. See here. It is extremely difficult to pinpoint the inspiration for this letter, but here are a few notable events in December 1969.
The first being the murder of Meredith Hunter at the Altamont Free Concert on December 6th 1969 at the hands of Hells Angel Alan Passaro, who fatally stabbed and beat the 18-year-old to death after he produced a revolver. This is not insinuating Alan Passaro was the Zodiac Killer, but bearing in mind the Hells Angels connection on Warren Avenue, Vallejo, and the drugs bust at The Cottage on Lake Herman Road in the run-up to the murders of David Faraday and Betty Lou Jensen, it was worth mentioning. Alan Passaro was later cleared of the murder having deemed to have acted in self defense.
On the political front, bearing in mind the author was threatening to go for 'government life,' was the author referencing the troubles of the day. On December 1st 1969 the Selective Service System of the United States conducted two lotteries to determine the order of call to military service in the Vietnam War for men born from 1944 to 1950. These lotteries occurred during a period of conscription from just before World War II to 1973. It was the first time a lottery system had been used to select men for military service since 1942. The lottery numbers assigned in December 1969 were used during calendar year 1970 both to call for induction and to call for physical examination, a preliminary call covering more men. Taken from Wikipedia. For those believing in a Vietnam or military connection to Zodiac, was he responding with outrage to this lottery based conscription- threatening to attack 'government life'.
On December 12th 1969, the Desert Sun ran an article about 'Two Attorneys Jailed in Tate Murder Case.'
District Judge David Brown today sentenced two Los Angeles lawyers to 72 hours in jail and fined them $lOO each for trying to make a “press spectacular” out of the case of Charles D. Watson, charged in the Sharon Tate murders. "I am fining you $lOO and jailing you for 72 hours but I will suspend this provided you take the next plane back to California and shut your mouths,” Brown told the attorneys, Perry Walshin and David DeLoach. “I admonish you for making a circus out of my courtroom,” said the judge. Watson, dressed in green work clothes, made his first public appearance since he gave himself up Nov. 30 in I answer to a California murder I warrant. He since has been indicted on seven counts of murder and one count of conspiracy. Susan Denise Atkins, another, of a hippie band charged in the California murders, told a grand jury Watson was the one who killed Miss Tate with a knife. “Do you want to talk to these men or be represented by them" Judge Brown asked Watson today about the two California lawyers. “No, sir, I do not,” Watson said. “Do you want to see them” Brown asked. “No, I do not,” Watson replied. At least 30 Texas highway 1 patrolmen guarded Watson. At least 20 patrolmen and sheriffs deputies were in the courtroom. Watson, who grew up at nearby Copeville, Tex., was moved into the courtroom before 6:30 a. m. and no reporters or photographers were allowed near him. Leaving the courtroom, officers threw a coat over Watson’s head and hustled him past photographers. Walshin and DeLoach came to Texas last week. Walshin said he had represented Watson on the coast and that Watson’s mother wanted him in the case. link.
This article was published four days before the Fairfield letter and eight days before Zodiac's letter to attorney Melvin Belli.
Was the Fairfield letter actually written by somebody connected with the Manson Family, or an avid follower of the unfolding events? Tex Watson would ultimately be convicted of the seven counts of first degree murder he was charged with. These are three unlikely examples of a possible inspiration for the Fairfield letter. Please post any further ideas in comments.