The mystery surrounding the Zodiac case also continues to fascinate the public and has inspired more than its fair share of theories regarding the killer’s identity.

Over the years, more than 2,500 suspects were considered, ranging as far afield as Unabomber Ted Kaczynski. A search warrant was executed for one prime suspect, Arthur Leigh Allen, but no definitive evidence was discovered. In addition, Allen's fingerprints did not match prints from Stine's taxi, and in 2002, DNA pulled from a Zodiac-sent stamp did not match Allen's. However, the DNA sample was small and the results somewhat inconclusive — plus Allen often had other people lick stamps for him.

Today's more advanced DNA techniques offer the tantalizing possibility of a definitive answer regarding who the Zodiac is, or was. But police in the 1960s and '70s had no idea that DNA analysis would arrive on the scene. Therefore some evidence was mishandled, or the chain of custody was broken. And pieces of evidence remain spread across various law enforcement agencies. In short, few things are available to analyze.

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