Someone asked why the case was reopened and I dug up this old article.

http://www.sfexaminer.com/sanfrancisco/police-to-re-examine-zodiac-killer-evidence/Content?oid=2155041

The most interesting part is that it says VPD was going to DNA test the letters. That’s news to me.

Vallejo Lt. Rick Nichelman said the SFPD has returned a number of envelopes — possibly those tested in 2002 during the investigation of one suspect, Arthur Leigh Allen, who died in 1992 — to Vallejo for further testing.

"DNA testing of five years ago is not as efficient as it is now," Nichelman said. "It was not as good of a sample as they can test now."