The FBI needs your help with this Zodiac killer message

Question

During a recent thorough cleanup round at the main building of the San Fransisco Chronicle, an employee found a piece of paper stuck behind an archive closet in one of the many archive rooms.

Her initial reaction was to discard it, just like had been the fate of many other documents that day. Somehow though, this particular sheet drew her attention because it vaguely reminded her of something she had seen in the news a long time ago.

Wasn't it something with some serial killer who used to write encrypted messages and pressured newspapers to publish them? She couldn't tell how long the piece of paper had been lying there, but to be on the safe side, she notified her supervisor who in turn called in his manager.

Indeed the document was resembling the code that the Zodiac killer used in his messages sent to the Chronicle in the late 1960s and early 1970s. The Zodiac killer had never been caught, so who knows what valuable information this newly found document might hold?

The note was sent to the Federal Bureau of Investigation, who immediately reopened the cold case and started a thorough investigation, putting their best cryptanalysts on the project.

Few months later, all attempts to decipher the message had unfortunately failed, therefore the FBI is now turning to the Puzzling Stack Exchange community with the following message:

Please, anybody: help us with deciphering this message as we may be one step closer to finally knowing the true identity of the Zodiac killer!

Attached are:

1. A photograph of the front of the page, containing the encrypted message.

2. A photograph of the back of the same page, containing some of the same characters used on the front page, written in a circular form. It is unclear if this is part of the message, or part of the key, or something else that we overlooked.

Answer 1

The killer's identity is

Ted Cruz

Solve path:

The diagram with twelve segments on the back seems to correspond to the names of the Zodiac signs, with each segment having the correct number of symbols for the signs and in the proper order. Print the names above the symbols.

Use the symbol-to-letter associations from the diagram to substitute most of the symbols.

Recall that the Zodiac 340-character cipher turned out to use a kind of "knight's-move" reading order for the letters. First, the text is divided into blocks of 9 lines. The first letter is at the top left of the block, and each following letter is one position below and two positions to the right. When moving below or to the right of the edges of the block, wrap around to the opposite side. The first few letters are I?OPE?O?. Recall the deciphered text of the Z340 cipher, which begins I HOPE YOU ARE HAVING LOTS OF FUN. Assuming this phrase gives a wealth of symbols, and the gaps in the ciphertext are quickly filled in.

When the plaintext is finally read, it seems to be directions for completing the puzzle.

i hope you are having lots of fun in trying to solve this puzzle to be fair and square i despice being anonymous because i like being in the spotlight too much therefore i am willing to reveal my identity to the puzzler that is willing to square their shoulders and remove all forward and backward written alphabetic characters from this cipher text then rearrange be precice and to finalice you should visualice

The "forward and backward written alphabetic characters" are identified. It is unclear whether the rest of the puzzle is contained in these letters, or in the letters that remain after removing them.

Transcribe the substituted ciphertext, while using uppercase letters to stand for the symbols in question. Count the remaining lowercase letters to find 225, a square number.

The word "square" appears twice in the instructions, which suggests the remaining letters are the next subject. Blank out the alphabetic characters.

Refuse to believe that the puzzle is asking to rearrange the remaining symbols into a 15x15 square. Attempt other approaches. Finally, transcribe the remaining symbols using placeholder letters (assigning A to the first symbol and all its occurrences, B to the second symbol, and so on).

Identify that the placeholder letters for the square symbols are CDEFR. Print the transcription in lines 15 letters long, while highlighting those letters to reveal the solution.

Easter eggs:

The plaintext contains the words "despice precice finalice visualice" which call back to the repeated misspelling in the Z340 cipher, spelling "paradise" as "paradice".

The name of David Oranchak, one of the codebreakers who solved the Z340 cipher in 2020, appears on the seventh line:

The ninth line has too many alphabetic symbols, and might have some secret meaning:

The 14th line appears to say LET'S CRACK:

The 20th line appears to say YOUTUBE in reverse. If there is a youtube video link lurking in here, I'm not inclined to search for it.

Is this a... bear?

I suspect there are more. Maybe focusing on the alphabetic symbols will help to find them: