A Vigenère Solution to the Zodiac Killer's Z13 Cipher: MY NAME IS LEIGH

THE BREAKTHROUGH: Nobody in 55 years treated "My name is" as part of the encrypted message. Every previous attempt assumed the 13 cipher characters contained a complete name. They don't. "My name is" IS the plaintext for columns 1–8. The cipher only hides 5 characters — a single first name.

THE METHOD: Treating "My name is" as a known-plaintext crib (the same methodology that cracked the Zodiac's Z408 and Enigma at Bletchley Park), Vigenère key values are computed at every letter position by simple subtraction. The back-half key values produce a perfect U-F alternation — an Atbash mirror pair (U+F=25). This pattern forces the final three plaintext letters to be I, G, H. The only 5-letter English name ending in IGH is LEIGH.

THE VERIFICATION: Plugging L and E into the remaining positions produces key values F and U — continuing the UFUF alternation with zero contradictions. All 8 letter positions verify. All 5 symbol positions produce consistent values. The ⊛ (Taurus) symbol encrypts to Q at all three of its occurrences. 8 + 5 = 13: every position accounted for.

THE TESTING: 4,388 candidate names tested — only LEIGH produces the UFUF pattern. 1,125 intro phrase + name combinations tested — only MY NAME IS + LEIGH produces an Atbash-paired alternating key. 306 suspect name variations tested (Marshall, Kane, Gaikowski, Poste, Van Best, Sullivan, Doerr, Kaczynski, Tucker) — zero produce UFUF.

THE NAME: LEIGH is the legal middle name of Arthur Leigh Allen (1933–1992), the only suspect ever publicly named by police in the Zodiac investigation. Allen was first interviewed as a suspect six months before Z13 was sent.

Both cryptographic techniques (Vigenère and Atbash) appear in David Kahn's "The Codebreakers" (1967), Chapters 2 and 5 — a book connected to the Zodiac investigation. The cipher escalation across all four Zodiac ciphers tracks the chapter progression of that book.

The full document includes step-by-step derivation, complete verification tables, competitive testing methodology, symbol resolution, suspect alignment with forensic exclusion evidence, and a detailed comparison with all competing Z13 solutions (Bauer's ALFRED E NEUMAN, Ziraoui's KAYR, Garlick's DR EAT A TORPEDO).

Submitted to the FBI on March 23, 2026. Published to establish priority and invite independent review.

*v2 contains the most up-to-date document*