[Toughluck_freeper]

I read it had already been solved.
The few extra symbols at the bottom of the first letter decoded to an anagram of his name.

And someone else decoded the other letters as well, showing the same name.

Turned out to be one of the suspects, Arthur Leigh Allen, already dead.

http://www.tonypolito.com/zodiac.pdf

[PMAS]

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[mairdie]

Very interesting. Thanks for the link.