Zodiackillersite.com

The statement at the bottom of the Bus Bomb Letter reads "To prove that I am the Zodiac, ask the Vallejo cop about my electric gun sight which I used to start my collecting of slaves."
The Vallejo Cop he is referring to is Jack E Stiltz, a Vallejo police chief.
http://www.zodiacciphers.com/zodiac-news/january-09th-2016

Yes, I believe it was in response to those articles.

Tahoe27 wrote:Yes, I believe it was in response to those articles.

Yes definitely and the statement "To prove that I am the Zodiac, ask the Vallejo cop about my electric gun sight which I used to start my collecting of slaves." was thought to be an interaction of some kind, as opposed to the Zodiac simply referencing his response to Jack Stiltz in the Debut Letter.