Zodiac Killer Ciphers Explained: Z340, Z13 and Z32 Mystery
Image Disclaimer
AI-Generated Illustrations: images used in our articles are AI-generated illustrations created for visual and educational purposes. They are intended to represent or recreate the people, locations, events, objects, or scenes discussed in the article and should not be considered authentic photographs, original evidence, or official documentation of the case. Where original photographs or copyrighted material exist, we may use AI-generated illustrations instead to avoid unauthorized use of copyrighted images. These illustrations are created based on publicly available descriptions, historical records, reports, and other information related to the case.
The Zodiac Killer and the Beginning of the Cipher Mystery
The Zodiac Killer was the name adopted by an unidentified person who sent a series of letters and cryptograms to newspapers in Northern California during the late 1960s and early 1970s.
The writer became particularly famous for combining criminal claims with deliberately mysterious communications.
The first major batch of letters arrived on July 31, 1969, when letters were sent to the San Francisco Chronicle, San Francisco Examiner and Vallejo Times-Herald.
Each newspaper received part of a much larger cipher.
The writer demanded that the newspapers publish the material, threatening further consequences if they did not.
The three sections eventually formed what is now called the Z408 cipher.
This was the beginning of one of the most famous cryptographic mysteries in American history.
What Made the Zodiac Ciphers Different?
The Zodiac communications were unusual because they were not simply coded messages.
They combined:
- strange symbols
- letters
- numbers
- repeated characters
- newspaper correspondence
- cryptographic puzzles
- maps
- claims about the writer's crimes
- references to future messages
- challenges directed toward police and the public
The symbols also varied considerably.
Some resembled ordinary alphabetic characters, while others looked like geometric shapes, crosshairs, astronomical symbols and specially constructed marks.
This made the messages visually distinctive and contributed enormously to the Zodiac mystery.
The Four Major Zodiac Ciphers
Four ciphers are usually regarded as the major Zodiac cryptograms:
Z408 — 408 characters — solved in 1969
Z340 — 340 characters — solved in 2020
Z13 — 13 characters — still unresolved
Z32 — 32 characters — still unresolved
There are also other Zodiac communications and cards containing unusual symbols or possible hidden messages, but these four are the central cryptographic puzzles discussed by researchers.
The Z408 Cipher — The First Major Code
The first major Zodiac cipher consisted of 408 characters.
Rather than sending the complete cipher to one newspaper, the writer divided it into three portions.
One portion went to the San Francisco Chronicle.
Another went to the San Francisco Examiner.
The third went to the Vallejo Times-Herald.
The newspapers published the sections, allowing readers to reconstruct the complete message.
This turned the cipher into a public puzzle.
Who Solved Z408?
The solution came surprisingly quickly.
A California schoolteacher, Donald Gene Harden, and his wife, Bettye June Harden, worked on the cipher after seeing the published material.
They eventually reconstructed the message.
Their solution was essentially a substitution system in which the Zodiac used numerous symbols to represent letters.
The Harden solution was published in newspapers in August 1969.
The decoded message contained the writer's disturbing explanation for why he claimed to kill and included references to his belief that his victims would become his "slaves" after death.
Importantly, however, the message did not reveal the writer's name.
That became a recurring pattern throughout the Zodiac cipher mystery.
The first major code was solved, but the identity question remained unanswered.
Why Z408 Did Not Solve the Zodiac Mystery
One of the biggest misconceptions about the Zodiac ciphers is that solving a cipher should automatically reveal the killer.
That did not happen.
The Z408 plaintext contained information about the writer's motives and worldview, but no reliable identification of the person behind the letters.
This meant that even after the first cipher was broken, investigators were still dealing with an unidentified writer.
And then came a much harder challenge.
The Z340 Cipher
On November 8, 1969, the Zodiac sent another coded message to the San Francisco Chronicle.
It contained 340 symbols arranged in a grid.
Researchers eventually called it Z340 or the 340 Cipher.
Unlike Z408, this cipher resisted attempts to solve it for decades.
For more than half a century, amateur codebreakers, professional cryptographers, computer scientists and Zodiac researchers attempted to understand its structure.
The message became one of the most famous unsolved cryptograms in the world.
The San Francisco Chronicle's archives contain historical material documenting the correspondence and cipher investigation.
Why Was Z340 So Difficult?
Z340 looked superficially similar to Z408 because it also used repeated symbols and unusual characters.
But the underlying construction was substantially more complicated.
Researchers eventually discovered that the cipher combined transposition with a homophonic substitution system.
In simple terms, the symbols did not simply correspond directly to letters in a straightforward one-to-one manner.
The arrangement of the characters themselves also mattered.
The way the grid was read had to be understood before the substitution system could be properly interpreted.
That combination helped keep the cipher hidden for 51 years.
The eventual academic paper describing the solution identifies the cipher as a transposition and homophonic substitution system with unusual characteristics.
The 51-Year Wait
For decades, Z340 became the centerpiece of Zodiac cryptography.
Many people claimed to have solved it.
Most proposed solutions failed because they could not demonstrate that the proposed plaintext was uniquely supported by the cipher.
A genuine cryptographic solution needs more than producing English-looking words.
It must explain the entire cipher using a reproducible method.
This distinction became extremely important because the Zodiac's shorter ciphers produced enormous numbers of possible interpretations.
The 2020 Z340 Breakthrough
In December 2020, an international team finally produced a convincing solution to Z340.
The team consisted of:
- David Oranchak, an American computer programmer and cryptography researcher
- Sam Blake, an Australian mathematician
- Jarl Van Eycke, a Belgian programmer
The solution was subsequently verified by the FBI.
The breakthrough ended a 51-year cryptographic mystery.
How Z340 Was Solved
The solution was not simply a matter of replacing symbols with letters.
The researchers discovered that the cipher involved multiple layers.
A major part of the solution involved determining how the characters had been rearranged within the grid.
The plaintext was then recovered using a combination of cryptanalytic techniques, including substitution analysis and computational search.
The researchers used software to explore enormous numbers of possible configurations.
This was a major difference from the original 1969 attempts.
Modern computing allowed researchers to test possibilities at a scale that would have been practically impossible by hand.
The detailed methodology is documented in the researchers' published paper.
What Did the Z340 Cipher Say?
The decoded message begins with the writer addressing people who were trying to catch him.
It includes the famous statement:
"I hope you are having lots of fun in trying to catch me."
The message also discusses the writer's apparent belief that he would receive some kind of afterlife reward for killing people.
It refers to the gas chamber and contains a statement denying that he was the person who appeared on a television program.
The message ends with a series of unusual statements and misspellings.
Most importantly, the Z340 solution did not reveal the Zodiac Killer's identity.
That was one of the biggest disappointments for people who had expected the 51-year-old cipher to finally expose the person behind the Zodiac letters.
What the Z340 Solution Proved
The successful solution demonstrated several important things.
First, the Zodiac really was capable of constructing relatively complicated cryptographic messages.
Second, the apparent randomness of the symbols concealed a structured system.
Third, the writer deliberately designed at least some of his ciphers to resist straightforward analysis.
And finally, solving the code did not necessarily mean solving the identity mystery.
Z340 gave researchers more information about the writer's communications, but it did not provide the definitive name everyone hoped to find.
The Z13 Cipher — "My Name Is..."
The next major mystery is considerably shorter.
It contains only 13 characters.
It is generally called Z13 or the "My Name Is" cipher.
It appeared in a Zodiac letter dated April 20, 1970.
The letter introduced the cipher with wording equivalent to:
"My name is—"
That made researchers immediately suspect that the 13 symbols might represent the writer's real name.
If that interpretation is correct, Z13 could potentially be one of the most important pieces of evidence in the entire Zodiac case.
There is one enormous problem.
There are only 13 symbols.
Why Z13 Is So Difficult
Short ciphers are extremely difficult to validate.
Imagine someone gives you thirteen symbols and asks you to determine a person's name.
There are countless ways to construct a mapping that produces a plausible name.
The shorter the message, the fewer repeated patterns there are available to test.
That means a person can sometimes create a proposed "solution" that looks convincing without actually proving that the Zodiac intended it.
This is why researchers generally demand much stronger evidence before accepting a Z13 solution.
The current specialist literature continues to classify Z13 as unsolved.
The Biggest Problem With Z13 Solutions
Suppose someone proposes that Z13 spells a particular person's name.
That alone does not establish that the person was the Zodiac.
A convincing solution would need to explain:
- why each symbol represents the proposed character
- why the cipher's structure supports the interpretation
- why alternative names are rejected
- whether the same cryptographic system appears elsewhere
- whether the solution is reproducible
- whether independent researchers can obtain the same result
Without those tests, almost any short cipher can become a vehicle for confirmation bias.
This is one of the reasons responsible Zodiac research avoids declaring a suspect identified simply because somebody has found a name that fits 13 symbols.
Recent Claims About Z13
The Z13 mystery continues to attract new proposed solutions.
Some modern researchers have used computer programs, artificial intelligence and large-scale searches to generate possible interpretations.
However, a proposed solution is not the same thing as an accepted solution.
As of 2026, the established specialist reference material still lists Z13 as unsolved.
There have also been recent claims connecting Z13 to specific individuals. These should be treated particularly carefully because a cryptographic claim alone cannot establish that a person committed a crime.
For a website intended for general readers and advertising platforms, it is much safer and more accurate to describe such ideas as unverified proposals, not discoveries.
The Z32 Cipher — The Mount Diablo Mystery
The fourth major cipher is called Z32.
It contains 32 symbols.
It was sent in connection with a map and a letter in June 1970.
Unlike Z13, the surrounding material gives researchers additional clues about what the cipher might have represented.
The writer connected the message to a map and discussed a possible location associated with a future attack.
The map prominently features Mount Diablo and contains instructions involving radians and inches.
Because of this context, researchers have generally interpreted Z32 as a possible location or map code.
But the exact meaning remains unproven.
Why Z32 Is Still So Difficult
Z32 has the same fundamental problem as Z13: it is extremely short.
It contains only 32 characters.
There are relatively few repeated symbols.
That means there are not enough internal patterns to easily determine which proposed decoding is correct.
Researchers can construct many possible interpretations.
The difficult part is proving that one interpretation is uniquely supported by the evidence.
The Zodiac Ciphers research community continues to classify Z32 as unresolved.
The Mount Diablo Theory
One of the major ideas surrounding Z32 is that it could identify the location of a bomb or another object.
The writer supplied a map and gave clues involving:
- Mount Diablo
- radians
- inches
- a particular map
- directional information
This has led researchers to believe that the cipher might have been intended as a geographic instruction.
However, no generally accepted decoding has established a definitive location.
Some researchers have proposed coordinates, distances and routes.
Others argue that the available information is insufficient to uniquely determine the intended location.
Therefore, the safest conclusion is that Z32 appears to have been associated with a geographic puzzle, but its actual plaintext and intended location have not been conclusively established.
Modern Attempts to Solve Z32
Z32 continues to attract independent researchers.
Some recent computational projects have claimed proposed solutions.
For example, one 2026 independent project published a proposed plaintext and argued that it points toward the La Honda area. However, the project's own materials describe it as a proposed solution, while other current research explicitly continues to classify Z32 as unsolved.
This disagreement is important.
It demonstrates why the existence of a published "solution" does not automatically mean the cryptographic community has accepted it.
For this reason, a responsible article should not state that Z32 has been solved.
Could Z13 and Z32 Have Been Designed to Be Impossible to Solve?
This is one of the more interesting theories.
Some researchers have suggested that the Zodiac deliberately created extremely short ciphers because he understood that they would be difficult to verify.
There is also a possibility that the writer himself was not following a perfectly consistent cryptographic system.
Another possibility is that the messages contained incomplete, deliberately ambiguous or misleading information.
Recent independent research has even argued that Z13 and Z32 may be structurally underdetermined rather than simply waiting for someone to discover a missing key. These are research interpretations, not established conclusions.
The "Zodiac Was a Cryptographic Genius" Theory
The successful Z340 solution has sometimes encouraged the idea that the Zodiac must have been an exceptionally skilled cryptographer.
The evidence is more complicated.
The writer clearly understood enough about codes and symbols to construct difficult messages.
However, there is no reliable evidence proving that he was a professional cryptographer or mathematical expert.
Z340's complexity may reflect deliberate construction, experimentation, knowledge obtained from existing cryptographic techniques, or a combination of these.
The fact that modern researchers required computer-assisted methods to solve it does not necessarily mean the original author was a mathematical genius.
The "Zodiac Wanted Attention" Theory
Another widely discussed interpretation is that the ciphers were partly designed to generate publicity.
The writer repeatedly communicated with newspapers.
He demanded publication.
He challenged police.
He referred to himself repeatedly.
He appeared to enjoy the public reaction surrounding the mystery.
From this perspective, the ciphers may have served two purposes:
communication and psychological manipulation.
The codes created a puzzle that encouraged newspapers, police, amateur investigators and the public to keep discussing him.
The mystery therefore continued even when the actual attacks had stopped.
The "The Ciphers Contain His Identity" Theory
This is particularly popular because of Z13.
The phrase introducing the cipher strongly encouraged the idea that the 13 symbols represented a name.
If that was genuinely the purpose, then solving Z13 could theoretically provide a major breakthrough.
But there is an important distinction:
A name that fits the cipher is not automatically the identity of the Zodiac.
Even a mathematically elegant decoding would still need to be compared with independent evidence from the investigation.
This distinction is especially important when discussing suspects.
The "Z13 Was Deliberately Too Short" Theory
Another possibility is that the Zodiac intentionally created Z13 so that it could never be conclusively solved.
With only 13 symbols, the writer could create a puzzle that looked meaningful while leaving enough ambiguity for endless speculation.
If that was intentional, then the mystery itself could have been the point.
There is no direct evidence proving this theory, but the extreme shortness of Z13 makes it a reasonable cryptographic question.
The "Z32 Was a Real Bomb Location" Theory
The Zodiac claimed that the Z32 message could lead to a location connected to a bomb.
This has generated decades of searches and interpretations.
Some researchers believe the map and wording suggest that the writer genuinely intended investigators to locate something.
Others suspect the entire puzzle may have been another attempt to generate publicity and fear.
There is no verified discovery of a Zodiac bomb location produced by solving Z32.
Therefore, the claim should remain categorized as part of the historical correspondence rather than established fact.
The "The Zodiac Made Mistakes" Theory
Not every unusual feature of the ciphers necessarily represents an intentional hidden trick.
The writer may have made mistakes.
The messages contain unusual spelling and inconsistent construction.
A cryptographic system can also become difficult to solve because of errors made by the creator.
If the Zodiac accidentally introduced mistakes into Z13 or Z32, a perfect mathematical solution might not exist.
This possibility is one reason researchers have to consider whether the original message was intentionally complex or simply imperfect.
Could Z13 and Z32 Be Nonsense?
This possibility cannot be completely dismissed.
A short sequence of symbols can appear meaningful even when it was not designed to produce a unique plaintext.
However, the surrounding letters and maps indicate that the writer intended readers to believe the material contained a message.
Whether the underlying codes were fully functional, deliberately misleading, incomplete or constructed with errors remains uncertain.
There is currently no evidence that conclusively establishes that either cipher is meaningless.
The Zodiac Ciphers and Artificial Intelligence
Modern computing has transformed Zodiac research.
When Z340 was finally solved in 2020, computers played an important role in testing enormous numbers of possibilities.
Today, researchers can use:
- statistical analysis
- optimization algorithms
- machine learning
- large-scale symbol searches
- pattern recognition
- automated substitution testing
- computational cryptanalysis
AI can help generate and test hypotheses, but it also creates a major problem.
A computer can find patterns that look convincing by chance.
Therefore, an AI-generated "solution" is not automatically a genuine decoding.
The solution must be independently reproducible and supported by the cipher's structure.
Why Z340 Is Different From Z13 and Z32
This distinction is extremely important.
Z340 contained hundreds of symbols.
That gave researchers a large statistical sample.
Repeated symbols and structural patterns could be tested.
Z13 contains only 13 characters.
Z32 contains only 32.
That dramatically reduces the amount of information available for cryptanalysis.
In other words, solving Z340 does not mean that Z13 and Z32 should be equally easy to solve.
Their mathematical problems are fundamentally different.
The Zodiac's Other Messages
The cipher story does not exist separately from the wider Zodiac correspondence.
The writer sent numerous letters, postcards and cards to newspapers.
The San Francisco Chronicle has documented 22 known Zodiac letters, with 17 sent to the Chronicle itself.
Not every communication was a cipher.
Some consisted mainly of threats, claims, symbols, drawings or cryptic references.
The writer continued communicating for years after the confirmed 1969 attacks.
The Chronicle's historical archive preserves extensive material from this period.
The Zodiac Symbol
One of the writer's most recognizable features was the crosshair-like symbol he used to sign communications.
The symbol became strongly associated with the name "Zodiac."
The writer first used the name Zodiac in an August 1969 letter.
The exact reason he chose that name remains unknown.
Was Every Letter Really Written by the Zodiac?
No.
This is an important part of the case.
Some later letters have been questioned by researchers and investigators.
The authenticity of certain communications remains disputed.
For example, a 1978 letter was considered genuine by some people and a possible hoax by others.
There were also later communications claiming to be from Zodiac.
Therefore, researchers distinguish between:
authenticated or strongly attributed communications
and
disputed or questionable communications.
That distinction is essential when reconstructing the case.
The Connection Between the Ciphers and the Murders
The Zodiac ciphers are often discussed as if they independently prove the identity of the writer.
They do not.
The letters and ciphers were connected to the Zodiac investigation because the writer claimed responsibility for crimes and because some communications contained information that investigators considered significant.
Law enforcement officially attributed five killings to the Zodiac, although the writer claimed a higher number of victims.
Other killings and disappearances have been suggested as possible Zodiac crimes, but those connections should not be presented as established fact without strong evidence.
Why People Became Obsessed With the Ciphers
The ciphers created an unusual combination of mystery and participation.
Readers could attempt to solve them themselves.
Newspapers published the symbols.
Amateur cryptographers worked on them.
Professional investigators studied them.
Later, computers were used.
The result was a mystery in which thousands of people could participate without needing access to police evidence.
That helped turn the Zodiac case into a cultural phenomenon.
The Biggest Misconception: "Z340 Revealed the Killer"
It did not.
The 2020 breakthrough solved the message, but the plaintext did not provide a reliable name.
This is one of the most important facts to include in any article about the Zodiac ciphers.
The solution was a cryptographic victory, not a definitive criminal identification.
The FBI verified the Z340 solution, but the Zodiac's identity remained unresolved.
What Has Actually Been Solved?
Z408
Status: SOLVED
Solved in 1969 by Donald and Bettye Harden.
The plaintext discusses the writer's motives and beliefs but does not reveal his identity.
Z340
Status: SOLVED
Solved in December 2020 by David Oranchak, Sam Blake and Jarl Van Eycke.
The solution was subsequently verified by the FBI.
It does not identify the Zodiac.
Z13
Status: UNSOLVED
The 13-character "My name is" cipher remains without a generally accepted solution.
Numerous proposed names and interpretations exist, but none has achieved the level of evidence required for acceptance.
Z32
Status: UNSOLVED
The 32-character map cipher remains unresolved.
Several proposed geographic solutions exist, including modern computational proposals, but no solution has achieved general acceptance.
What Do Cryptographers Think About the Unsolved Ciphers?
The most cautious position is that Z13 and Z32 may simply contain too little information to produce a unique answer.
A cryptographic message can be mathematically valid while still being impossible to uniquely recover if there is insufficient information.
This is particularly relevant to Z13.
With only 13 symbols, researchers cannot rely on the same statistical methods that helped with Z340.
Z32 has more characters but still suffers from limited repetition and the additional uncertainty introduced by the map.
Therefore, a successful future solution would need to demonstrate much more than a plausible phrase.
Theories About the Identity Behind the Ciphers
The cipher mystery has naturally become connected to theories about who the Zodiac was.
Over the decades, numerous suspects have been proposed.
One of the best-known was Arthur Leigh Allen, who was investigated and became the subject of extensive public speculation.
However, Allen was never convicted as the Zodiac, and the identity of the killer remains officially unresolved.
The San Francisco Chronicle has documented the long history of suspect theories and emphasizes that the case remains unsolved.
For responsible reporting, it is important not to present an unproven suspect as the murderer.
Could the Ciphers Still Be Solved?
Yes, but that does not mean they necessarily will be.
A genuine solution to Z13 or Z32 would probably need several independent forms of confirmation.
Researchers would ideally want:
- a consistent cryptographic method
- a complete plaintext
- an explanation for every symbol
- reproducible calculations
- consistency with known Zodiac communications
- rejection of reasonable alternative solutions
- independent verification by other researchers
Simply producing a name or location is not enough.
The Most Interesting Possibility
Perhaps the most fascinating aspect of the Zodiac cipher story is that the biggest breakthrough did not come from discovering a secret government file or a hidden confession.
It came from people who spent years studying the structure of the symbols.
The Z340 solution demonstrates that a message that appears impossible to understand can sometimes yield to careful cryptanalysis and modern computation.
But it also demonstrates something equally important:
Solving a code does not necessarily solve the mystery surrounding its author.
What We Know and What We Don't Know
What is established
The Zodiac writer sent coded communications to Bay Area newspapers.
The 408-character cipher was solved in 1969.
The 340-character cipher was solved in 2020 after remaining unresolved for 51 years.
The Z340 solution was verified by the FBI.
Z13 remains unresolved.
Z32 remains unresolved.
The ciphers did not conclusively reveal the Zodiac's identity.
What remains unknown
The true identity of the Zodiac remains unresolved.
The definitive meaning of Z13 remains unknown.
The definitive meaning of Z32 remains unknown.
It is unknown whether either short cipher contains a uniquely recoverable message.
It is also unknown whether the writer deliberately designed the short ciphers to be ambiguous.
Why the Zodiac Ciphers Still Matter
The Zodiac ciphers remain important not simply because they are connected to a notorious criminal investigation.
They represent a rare intersection of:
cryptography + journalism + criminal investigation + psychology + computer science + public participation.
Z340 demonstrated how modern computational methods can eventually solve a cryptographic puzzle that resisted analysis for more than half a century.
Z13 and Z32 demonstrate the opposite problem: sometimes there may simply not be enough information to establish one answer with confidence.
That tension is what keeps the Zodiac cipher mystery alive.
The Bottom Line
The Zodiac Killer's ciphers are not all unsolved.
Z408 was solved in 1969.
Z340 was solved in 2020 after 51 years.
Z13 remains unsolved.
Z32 remains unsolved.
And perhaps most importantly, none of the accepted cipher solutions has definitively identified the Zodiac Killer.
The remaining mystery is therefore not simply "What do the codes say?"
It is also whether the shortest codes can ever be proven to have one unique meaning.
Until that happens, claims that Z13 or Z32 have definitively revealed the killer should be treated as theories rather than established discoveries.
Real Sources, Original Records and Safe Websites
For a website article, I recommend prioritizing official archives, established newspapers, academic publications and institutional collections rather than conspiracy websites.
FBI Vault — Official Zodiac Killer Files
The FBI has released seven parts of its Zodiac Killer records through the FBI Vault. These are among the most important primary-source materials available online.
FBI Vault — The Zodiac Killer Files
San Francisco Chronicle — Zodiac Archive
The Chronicle has extensive historical material, including original newspaper coverage, letters, cipher reproductions and photographs from its archives.
San Francisco Chronicle — Zodiac Killer Archive
San Francisco Chronicle — Historical Coverage
This collection contains historical articles and reproductions of Zodiac communications from the original newspaper archive.
San Francisco Chronicle — Zodiac in Print Archive
FBI Records — Individual Zodiac File
The FBI Vault also provides individual PDF sections of the released investigation files.
Academic Paper on the Z340 Solution
The complete technical paper by David Oranchak, Sam Blake and Jarl Van Eycke explains how the 340-character cipher was solved.
The Solution of the Zodiac Killer's 340-Character Cipher
Zodiac Ciphers Wiki
This specialist research reference separates the solved Z408/Z340 ciphers from the still-unsolved Z13/Z32 material and documents proposed solutions and observations. It is useful as a research reference, but it is not an official law-enforcement source.
Z32 Cipher Reference
This page provides the historical Z32 cipher, map context and information about why the short code is difficult to solve.
Keywords:
Zodiac Killer ciphers, Zodiac Killer cipher, Zodiac 340 cipher, Z340 cipher, Zodiac Z13 cipher, Zodiac Z32 cipher, Zodiac Killer codes, Zodiac Killer unsolved ciphers Zodiac Killer, Zodiac cryptogram, Z408, Z340, Z13, Z32, Mount Diablo cipher, Zodiac letters, San Francisco Chronicle, FBI Zodiac files, Zodiac codebreaker, cryptography, criminal investigation, unsolved mystery, 1969 Zodiac cipher, 1970 Zodiac cipher, Zodiac investigation, historical cryptography, codebreaking mystery.