7. Ted Kaczynski
If the name Theodore Kaczynski doesn't ring a bell, then check your true crime credentials at the door. The hunt for the Zodiac killer became so desperate that officials resorted to investigating any known criminal as a potential suspect. That included the infamous Unabomber.
Ted Kaczynski started out in an academic career, displaying genius-level intelligence from a young age. However, disillusionment with modern living and a passion for environmentalism soon threw him off that path and towards an extreme lifestyle, living off-grid in a remote part of Montana. He soon became radicalised, embarking on an anti-industrialisation bombing campaign that killed three and injured many more.
Kaczynski wasn't arrested for his domestic terrorism until 1996, but his crimes ran from 1978 to 1995. Ted lived in the Bay Area during the Zodiac's prolific years, leading some to theorise that the Unabomber's spree may have started in 1967 with the killings. Kaczynski and the Zodiac share some habits: both wrote letters to papers, liked a code that needed to be cracked, and the Zodiac expressed great interest in bomb construction.
Despite the interesting coincidences, it seems that's all these unusual connections will ever be. It wasn't enough to pursue the concept any further, and Kaczynski adamantly denies any involvement.