Note the stamp depicting a taxi cab. (Zodiac's last definite victim was killed in a cab.)
Also contained in the envelope were fingerprints and DNA samples wrapped in packets that originally contained a toxic substance.
I'll post an update when I get more information.

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The DNA was enclosed in packets of a product called Tse Koo Choy.
Manufactured by WangHing Co., Ltd., in Hong Kong, its toxic ingredients include Mercurous chloride and santonin.
Adverse reactions include mental and sensory disturbances, mental deterioration, pink to red coloring of extremities,
tremor, nausea, vomiting, diarrhea, headache.