10 Reasons Why Zodiac Killer MAY Have Been Solved

Zodiac is famed for writing taunting letters and cards to regional California newspapers, and Doerr himself had a penchant for writing letters to his favourite "zines" (self-published magazines) and also publishing his own.

Due to many of the zines being digitised online, Kobek was able to track a trove of Doerr's written contributions, which bear marked similarities to Zodiac both in terms of content and writing style.

He's written letters making references to slavery - something Zodiac also wrote about as part of his apparent motive - and penned a letter to the SF Examiner without a street address, just as the Zodiac did. They also both wrote about something as esoteric as magnetic poles.

Furthermore, an anonymous letter written to one of Doerr's favourite zines - and believed to have been written by him - bears many superficial hallmarks of Zodiac's writing style, such as including seemingly intentional spelling mistakes and signing off with a symbol as a signature.

Like Zodiac, Doerr also enjoyed writing lists, used an ampersand instead of "and," often wrote sentences in all-caps except for lower-case i's, and occasionally used a circle to dot lower-case i's and punctuate sentences.

This is without getting into recurring language which can be seen in both Doerr and Zodiac's writing, which while hardly a smoking gun in its own right simply illustrates further shared characteristics between the two.