The Zodiac Killer quoted a portion from one of the three stanzas of The Mikado's Tit-Willow, when he mailed the 'Exorcist' letter on January 29th 1974. This may possibly have been the third correspondence, including the 'Halloween' card, where The Mikado was referenced. The Zodiac Killer began with the 'Little List' letter on July 26th 1970, in which he paraphrased 'As some day it may happen' featuring Ko-Ko the Lord High Executioner. In the letter he was effectively quoting the search for future victims as paralleling his agenda throughout the state of California. If we break down the 'Exorcist' letter into its constituent parts, it becomes apparent the correspondence is a further threat towards the citizens of California rather than a declaration of his impending suicide.
If we take a look at the October 27th 1970 'Halloween' card and compare it to his confirmed attacks, only one stands out. On September 27th 1969 Cecelia Shepard and Bryan Hartnell were relaxing by the shores of Lake Berryessa when a man spotted by Cecelia ducked behind a tree to don an executioner's mask and waistline bib. This theatrical entrance in the form of Ko-Ko the Lord High Executioner has long been suggested as an influence on the Zodiac's actions and writings. Here is an extract from the San Francisco Chronicle on October 12th 1970, just 15 days prior to the mailing of the 'Halloween' card:
"It was immediately apparent that Zodiac had plagiarized several stanzas from an aria in the Gilbert and Sullivan operetta 'The Mikado'. It is the entrance aria of Ko-Ko, the Lord High Executioner. A quiet search of onetime Ko-Ko's has turned up none that could be Zodiac. Obvious differences in physical description and handwriting comparisons have cleared all Ko-Ko's tracked down since the arrival of the July 27 letters." 

The 'Halloween' card depicted an eye peering from the knothole of a tree, accompanied by the words 'peek-a-boo you are doomed', implying the impending threat of the Zodiac Killer hiding behind the tree at Lake Berryessa and his ultimate arrival bedecked in an executioner's outfit. If you look up the definition of peek-a-boo in Wikipedia, it quotes "Peekaboo (also spelled peek-a-boo) is a form of play primarily played with an infant. To play, one player hides their face, pops back into the view of the other, and says Peekaboo!, sometimes followed by I see you! There are many variations: for example, where trees are involved, "Hiding behind that tree!" is sometimes added." 
However, Peek-A- Boo was also a character in another version of The Mikado at around the same time as the Gilbert and Sullivan operetta. "In 1888 Jack the Ripper terrorized the Whitechapel district of London. In the same year of somewhat less significance Ed J. Smith wrote a stage parody called The Capitalist; or, The City of Fort Worth. Designed to encourage capital investment in Fort Worth, Texas, and underwritten by local banks and railroad lines, the two act piece features characters named Yankee-Doo, Kokonut, By-Gum and Peek-A-Boo." Here is an image depicting this reference.     

Peep-bo is the English version of peek-a-boo, and has a curious, albeit likely unintentional connection to the Lake Berryessa murder of Cecelia Shepard, in the nursery rhyme Little Bo-Peep.
​"The earliest record of this rhyme is in a manuscript of around 1805, which contains only the first verse. There are references to a children's game called "bo-peep", from the 16th century, including one in Shakespeare's King Lear (Act I Scene iv), for which "bo-peep" is thought to refer to the children's game of peek-a-boo, but no evidence that the rhyme existed earlier than the 18th century. The additional verses are first recorded in the earliest printed version in a version of Gammer Gurton's Garland or The Nursery Parnassus in 1810". Wikipedia.
Peep-bo was one of the three little maids from The Mikado: "Three little maids from school are we, pert as a school-girl well can be, filled to the brim with girlish glee, three little maids from school." 

Three young girls from Pacific Union College would feature in the Zodiac story of Lake Berryessa that day, when describing a suspicious individual roaming the hillsides surrounding the lake- later providing a sketch of the individual. 
Little Bo-Peep was a shepherdess, so its significance to the name of Cecelia Shepard could not be ignored, although likely accidental. "She heaved a sigh and wiped her eye, and over the hillocks went rambling, and tried what she could, as a shepherdess should, to tack each again to its lambkin"
The Riverside murder of Cheri Jo Bates on October 30th 1966 and the subsequent 'Confession' letter held an odd precursor to the events of Lake Berryessa, when it stated "Miss Bates was stupid. She went to the slaughter like a lamb", along with the widely referenced "She squirmed and shook as I choked her, and her lips twitched" connection to the 'Little List' letter.  

​The Zodiac Killer, after mailing his response to the unearthed Riverside connection would then go into hibernation from March 13th 1971 until the arrival of the 'Exorcist' letter nearly three years later on January 29th 1974, leading many to believe the Zodiac Killer was likely incarcerated during this period. 
"Taken from the county jail
By a set of curious chances;
Liberated then on bail,
On my own recognizances;
Wafted by a favouring gale
As one sometimes is in trances,
To a height that few can scale."  Behold the Lord High Executioner Youtube
The Mikado/Act I/Part V
The Lord High Executioner was to return, berating the 1973 film 'The Exorcist,' yet curiously comparing it to the Gilbert and Sullivan's satirical operatic comedy, The Mikado, calling it "the best satirical comedy that I have ever seen."  He then signed his name using the verse of Tit-Willow by Ko-Ko: "He plunged himself into the billowy wave and an echo arose from the suicides grave, titwillo, titwillo, titwillo."
The whole letter was effectively announcing the return of the Lord High Executioner after nearly three years. Here is the 'Exorcist' letter broken down into its constituent parts to reveal its likely meaning.
"I saw and think "The Exorcist" was the best satirical comedy that I have ever seen, even better than The Mikado. Signed, yours truley: The Lord High Executioner. If I do not see this note in your paper, I will do something nasty, which you know I'm capable of doing- To Kill."
Kevin Robert Brooks came up with possibly the best interpretation of the Japanese/Asian symbols at the foot of the letter, befitting of Ko-Ko the Lord High Executioner. The "This is the Zodiac speaking" introduction was apparent by its absence, as well as the Zodiac crosshairs- but the Lord High Executioner was alive and well, and still making threats.  

The Zodiac Killer teased us with his name on more than one occasion, firstly in the July 31st 1969 San Francisco Chronicle letter where he stated "I want you to print this cipher on the front page of your paper. In this cipher is my idenity." He would follow this up with the 'My Name is...' letter on April 20th 1970 and the 'Halloween' card on October 27th 1970 tempting us with his name again; "I feel it in my bones, You ache to know my name, And so I'll clue you in.." 
​It would appear however, this was never to be the case and we are still no nearer to securing the identity of the Zodiac Killer nearly half a century later. It always seemed strange the Zodiac Killer would interpose the Gilbert and Sullivan Mikado into his correspondence, leading researchers to believe he was a fan of the theater, having quoted three acts of The Mikado in the 'Little List' letter of July 26th 1970 and 'Exorcist' letter of January 29th 1974. But there may be an ulterior motive behind this apparent fascination with Gilbert and Sullivan, in that the killer was using the Mikado to reveal his name, and likely through four mailings rather than the accepted two. We will take a closer look at these four correspondences and the speculative links between them, without claiming this is anything more than coincidence. Let us first look at the 'Exorcist' letter.   

The first thing to notice is its carefully structured appearance, being divided neatly into four sections of text. The curious thing about the correspondence is Zodiac wrote "Signed, yours truley," as though he was about to offer up his name in the third block of writing. He then recited ​Act II -On a tree by a river from The Mikado. It seemed like Zodiac was wasting our time, plucking out random verses from The Mikado, that is until you read verse three of this particular act. It not only contained a reference to 'name', but pointed us towards 'The My Name is...' cipher, mailed on April 20th 1970. Here is verse three.
Now I feel just as sure as I'm sure that my name
Isn't Willow, titwillow, titwillow,
That 'twas blighted affection that made him exclaim
"Oh, willow, titwillow, titwillow!"
And if you remain callous and obdurate, I
Shall perish as he did, and you will know why,
Though I probably shall not exclaim as I die,
"Oh, willow, titwillow, titwillow!"

Was the Zodiac Killer giving us clues to his identity or name, by leading us back to the '13 Symbol' cipher. This observation on its own is meaningless, so we will travel back in time to the 'Little List' letter mailed on July 26th 1970, the supposed only other correspondence to contain references to The Mikado- in fact two. The first section of the 'Little List' letter pulled lines from  'A more humane Mikado', and continued on to extensively recite Gilbert and Sullivan's Mikado Act One Part 5a  'As some day it may happen', performed by Ko-Ko. In the introductory part of the letter, Zodiac simply boasted about how he would torture his slaves in paradise, but he again did something curious, by selecting just one small section of 'A more humane Mikado,' despite it being ten verses in length. The same as he did in the 'Exorcist' letter. He then continued to paraphrase the entirety of 'As some day it may happen'.
The 'Exorcist' letter, we have shown to have tenuous links to the April 20th 1970 'My Name is...' letter, using verse three of 'Tit-Willow'. So let us look at the small section of text Zodiac selected from 'A more humane Mikado.'
The 'Little List' letter read "And all billiard players I shall have them play in a darkened dungen cell with crooked cues + Twisted Shoes."  Why does Zodiac select this small portion. Was this also hinting towards the 'My Name is...' cipher.
When we think of billiard players or billiard balls from the standpoint of America, eight-ball comes to mind, and the circled eights on the '13 Symbol' cipher. 

This is the full verse (right) from 'A more humane Mikado.' It is actually verse eight out of ten, providing us with the numerical link, as did verse three from the 'Exorcist' letter. The Zodiac Killer did state on the 'My Name is...' letter; "PS I hope you have fun trying to figgure out who I killed."​​​
There is however another link from 'A more humane Mikado,' to the alphabetical characters on the '13 Symbol' code mailed by Zodiac.
The Zodiac Killer supplied us with eight alphabetical characters, reading from left to right  A, E, N, K, M, N, A and M.
In the diagram below, key sections of 'A more humane Mikado' are highlighted for comparison to the '13 Symbol' cipher. Seven letters have been highlighted in green and yellow. This is where we must take a bold leap of faith, and consider that the Zodiac Killer chose The Mikado by Gilbert and Sullivan because it simply contained his name, Kim. Nothing more theatrical than that. 

The green highlighted sections on 'A more humane Mikado' in reverse, read KIMNAM. If we believe therefore, that the middle eight represents the letter I on the '13 Symbol' cipher, it reads forward KIMNAM, exactly the same. The remaining letters of the cipher AEN are shown highlighted in yellow. Every letter on the '13 Symbol' cipher is contained within this section of seven letters. 
​The three eights encapsulated his identity, just like the three eights at the foot of the '340' character cipher mailed on November 8th 1969: The Mathematics of the 13 Symbol Cipher. Who said the Magic 8 ball was just for telling fortunes! Additionally, Mikado can be formed using the alphabetical characters on the 20th line of the '340' cipher.
The Zodiac was keen to share with us what he had in store for his slaves in paradise:
"This is the Zodiac speaking. Being that you will not wear some nice buttons, how about wearing some nasty buttons. Or any kind of buttons that you can think up. If you do not wear any type of buttons, I shall (on top of everything else) torture all 13 of my slaves that I have waiting for me in Paradice. Some I shall tie over ant hills and watch them scream + twich and squirm. Others shall have pine splinters driven under their nails + then burned. Others shall be placed in cages + fed salt beef untill they are gorged then I shall listen to their pleass for water and I shall laugh at them. Others will hang by their thumbs + burn in the sun then I will rub them down with deep heat to warm them up. Others I shall skin them alive + let them run around screaming. And all billiard players I shall have them play in a darkened dungen cell with crooked cues + Twisted Shoes. Yes I shall have great fun inflicting the most delicious of pain to my slaves."
The talk of slaves, paradise, pine splinters, dungeons and hanging his 'prisoners' by the thumbs, catapulted me to the 'Halloween' card mailed on October 27th 1970, and the last Mikado installment. The Zodiac Killer placed some wording around the knothole in the tree:"peek a boo you are doomed." Bearing in mind that The Mikado opened to the paying public on March 14th 1885, and was hugely successful, running for 672 performances at the Savoy Theatre in London, a British connection had to be sought. The British term for peek-a-boo is peep-bo, and peep-bo is a character in The Mikado.      

The Halloween Card was mailed on October 27th 1970, one month after of the first Lake Berryessa anniversary, and one cannot help thinking the Zodiac Killer may have delayed this correspondence a short time, with Halloween providing the perfect backdrop to 'commemorate' his attack on Bryan Hartnell and Cecelia Shepard on the shores of Lake Berryessa, bearing in mind that dressing up in costumes is central to the All Hallows Eve festivities. 
Before the attack on the couple, Cecelia Shepard noticed the eventual assailant conceal himself behind a tree, before approaching them bedecked in his executioners costume and it has not gone unnoticed that the Halloween Card parallels this to some extent, with eyes peering from the tree and the phrase 'peek-a-boo you are doomed' circled around a knothole on the tree, along with the mask on the skeleton. The author of the card accentuates the section 'ME' of 'DOOMED', lending weight to the thought he was indeed referring to himself as the eyes behind the tree.

The Lamplighters, hailed as one of the oldest company's in the Bay Area, specializing in Gilbert and Sullivan, operated at the Harding Theater throughout the 1960's and were performing the Mikado in San Francisco in 1969, opening on April 20th. This connection is nothing new, with many speculating the Zodiac Killer could have been a cast member or had viewed the production, prior to his version, when he tabled in the Little List Letter on July 26th 1970. But it is equally likely he may have been a theater technician, employed in the area of stage management, lighting, electrics or quite possibly wardrobe, trained in costume design, as a tailor or more specifically wardrobe crafts involving masks and disguises.
In two other correspondences mailed by the Zodiac Killer he referenced three portions of Gilbert and Sullivan's Mikado. In the Little List Letter mailed on July 26th 1970 he paraphrases 'A more humane Mikado', plus 'As some day it may happen'. On the Exorcist Letter mailed on January 29th 1974 he refers to 'On a tree by a river', in what many believe to be the Zodiac Killer's final offering. But there could be a fourth reference to the Mikado production and we need look no further than the Halloween Card itself, with two possibilities.
In 1888 Jack the Ripper terrorized the Whitechapel district of London. In the same year of somewhat less significance Ed J. Smith wrote a stage parody called The Capitalist; or, The City of Fort Worth. Designed to encourage capital investment in Fort Worth, Texas, and underwritten by local banks and railroad lines, the two act piece features characters named Yankee-Doo, Kokonut, By-Gum and Peek-A-Boo. Taken from Wikipedia.
This drew its inspiration from the the Gilbert and Sullivan opera, however it may be pushing the boat out a little farther than necessary to suggest the Zodiac Killer was either aware or in any way influenced by this promotion.

One thing evident throughout his correspondence, was his use of the word 'shall', leading to speculation that he may have been of British origin, as the word 'shall', is infrequently used in American English, but another option exists. As a member of theater production, his exposure to the word 'shall' would have been far more common in the performance of stage plays, particularly in traditional works of English origin, but sought maximum impact when he took it to the next level and started crafting his own scripts.
Peek-a-boo is known as Peep-bo in British culture and is the act of concealing ones face behind the hands or other object, before suddenly appearing back into view and uttering the words peek-a-boo or peep-bo. It can be seen in Wikipedia that many variations involve trees, similar to the depiction on the Halloween Card, where 'Hiding behind that tree' is added. See here.
Whether or not it is a significant phrase by the Zodiac Killer is open to question, but Peep-Bo is a character that features during Act I of the Mikado.
Peep-bo can also be reversed to Bo-peep, believed to originate from the 16th century practice of concealment, before reappearing to startle or surprise. See here.   

Little Bo Peep is a popular English nursery rhyme The earliest record of this rhyme is in a manuscript of around 1805, which contains only the first verse. There are references to a children's game called "Bo-Peep", from the 16th century, including one in Shakespeare's King Lear (Act I Scene iv), but little evidence that the rhyme existed. The additional verses are first recorded in the earliest printed version in a version of Gammer Gurton's Garland or The Nursery Parnassus in 1810. The phrase "to play bo peep" was in use from the 14th century to refer to the punishment of being stood in a pillory. For example, in 1364, an ale-wife, Alice Causton, was convicted of giving short measure, for which crime she had to "play bo pepe thorowe a pillery". Andrew Boorde uses the same phrase in 1542, "And evyll bakers, the which doth nat make good breade of whete, but wyl myngle other corne with whete, or do nat order and seson hit, gyving good wegght, I would they myghte play bo pepe throwe a pyllery". Taken from Wikipedia.
Little Bo Peep was a shepherdess, who lost her sheep and went in search to find them. The connection of shepherd to the Lake Berryessa attack via this route would be one hell of a stretch, however the connection to the theater, with an English slant, still remains an avenue for investigation.

Waiting in the wings, the Zodiac Killer was not content with a supporting role, he yearned to have his name in the spotlight, however he was to act out his deep seated desire on a much grander scale, but unlike the theatrical tragedies that had gone before him, this one was to be performed on a very real stage, with dark consequences.  
This analysis searches into the mindset of the Zodiac Killer, taking his influences as the driving force behind the numerous letters he formulated over a period of nearly five years, exploring the wording and subject material he painstakingly orchestrated, to narrow down a profession that, above all, takes center stage.
It has been noted on countless occasions that the Zodiac Killer had leanings toward the dramatic, His early correspondence included part inference to The Most Dangerous Game, a short story by Richard Connell, published on January 19th 1924, as well as several references to the Gilbert and Sullivan comic opera, The Mikado, first viewed by the paying public on March 14th 1885. The Mikado featured heavily in his 'Little List' letter, mailed to the San Francisco Chronicle on July 26th 1970 and was resurrected in the 'Exorcist' letter, his last confirmed correspondence mailed on January 29th 1974.

The Lamplighters, hailed as one of the oldest companies in the Bay Area, specializing in Gilbert and Sullivan, operated at the Harding Theater throughout the 1960's and were performing the Mikado in San Francisco in 1969, opening on April 20th. This connection is nothing new, with many speculating the Zodiac Killer may have been a cast member or had viewed the production, prior to his version, when he tabled in the Little List Letter on July 26th 1970. But it is equally likely he may have been a theater technician, employed in the area of stage management, lighting, electrics or quite possibly wardrobe, trained in costume design, as a tailor or more specifically wardrobe crafts involving masks and disguises.
He claimed in his Bus Bomb Letter of November 9th 1969 ' The police shall never catch me, because I have been too clever for them.  I look like the description passed out only when I do my thing, the rest of the time I look entirle different. I shall not tell you what my descise consists of when I kill '.
He also made a grand appearance at Lake Berryessa on September 27th 1969, having either purchased, borrowed or crafted  
a black executioner's hood and a waistline bib, emblazoned with the Zodiac crosshairs, but either way his entrance was of theatrical proportions.
One thing evident throughout his correspondence, was his use of the word 'shall', leading to speculation that he may have been of British origin, as the word 'shall', is infrequently used in American English. However, another option exists. As a member of theater production, his exposure to the word 'shall' would have been far more common in the performance of stage plays, particularly in traditional works of English origin, which he would seek maximum impact, when he took it to the next level and started crafting his own scripts. 
Embittered by rejection, he mailed his work to the heart of the American people, seeking literary recognition, albeit only succeeded in creating a tragedy of epic proportions, while hiding behind a pseudonym that belies his cowardice.   

The Zodiac Killer mystery retains an unfaltering allure, that has managed to captivate a worldwide audience for more than four decades. When people become entranced with the case, there are many times upon reviewing the postcards, ciphers and wording, that the breath of the killer can almost be felt for a brief moment, when you spot something you think is significant, before it is cruelly snatched away. But it does not stop you trying, in essence to close the book on years of torment for the victims families and friends, which often has unfortunately become lost in the midst of this tragic affair.
Many suspects have been touted as the infamous Zodiac Killer, and most have been effectively eliminated from ongoing scrutiny. However, recently another name has emerged, that of Donald Lee Bujok, promoted from previous obscurity to the forefront of the discussion, by some detailed and extensive research by Zodiac enthusiast Kevin Robert Brooks, who can claim to have felt the breath of a killer more than most.

But can Kevin Robert Brooks convince us that Donald Lee Bujok is the killer. Well that is for you to decide.
As an introduction to this suspect, one must first acquaint themselves with the forerunner to this story, 'Donald Lee Bujok-Zodiac Suspect, which details the thought processes the killer used in the design of the Halloween Card.
Bearing in mind the killer is approaching his writings from a rationale different from the norm, the key to cracking his codes, may lie in unconventional thinking, held naturally by very few individuals. 
Kevin Robert Brooks also dissects the Exorcist Letter and subsequent S.L.A Letter, which he believes are inextricably linked by the word "kill".
It is a widely held belief that the footnote of the Exorcist Letter stating  Me-37 SFPD-0, is a reference to his murder count so far. If we believe that his 'tally' was progressive, who and where are all his victims, and why the three year period of inactivity in correspondence. If the killer was incarcerated during this period, then murder on this magnitude is frankly implausible, if we are to believe the Exorcist Letter as genuine Zodiac material.
​However, there is an alternative, in that the killer is revealing his age of 37 years, this time attributing it to Me, and not the Zodiac symbol as in previous writings. 

other schoolchildren, and ultimately becoming socially detached. 
Determined to lay claim to some meaning in life, Donald Lee Bujok joined the army, where in 1954 he was stationed at Fort Ord on Monterey Bay. This posting, according to Kevin Robert Brooks, effectively became pivotal in his later correspondence, manifesting itself  in the construction of The Halloween Card and envelope, detailed by Kevin Robert Brooks in a Youtube video and previous article on this site.
But another tantalizing clue lay in something Donald Lee Bujok could have retained from his brief spell at Fort Ord, before his medical discharge- this being the writing paper used at the military base.
This may possibly be the same paper used to author the Zodiac letter, sent to the San Francisco Chronicle on July 31st 1969, described on page 446 of Robert Graysmith's 'Zodiac Unmasked'. That being, it was so thin, that the overleaf became visible, measuring exactly 7 and 1/8 inches by 10 and 1/2 inches, identical to the Fort Ord stationary Donald Lee Bujok would have had access to. But after his early contact to the newspapers, wisely switched materials, in order to protect his identity.
Kevin Robert Brooks, crafted by careful research, is steadfast in his belief that his suspect is the Bay Area murderer, and is now more confident than ever, that the breath of his killer, is the one that condensed in the chill of the Lake Herman Road air on December 20th 1968.