ZKS  Hanging round the crime scene....
The Zodiac Killer has been inextricably linked to five murders and the four locations of Lake Herman Road, Blue Rock Springs Park, Lake Berryessa and Presidio Heights 
This forum thread by jamesmsv on October 26th 2013 considers the possibility that the Zodiac Killer may have remained behind after his crimes, observing from a safe distance.
It is not unheard of for criminals to hang around a crime scene and become the hidden face in the crowd.
jamesmsv states  'I was thinking about Z's descriptions of the Presidio Heights police activities and it got me thinking - what was the crowd situation there'.
To view the entire thread visit here.

ZKS  Darlene's Address Book
On Wednesday July 17th 2013 Quicktrader takes us back to the Blue Rock Springs Park murder of Darlene Ferrin and the attempted murder of Michael Mageau, at around midnight on July 4th 1969. The following day, some forty minutes after the attack, a phone call was received by police dispatcher Nancy Slover, who became the first person to hear the Zodiac Killer's menacing voice.
This thread takes a deeper search, in a bid to uncover any useful information that may have been stored within Darlene Ferrin's address book, hoping that one or more of the contacts, may unlock or unravel some key information for the motive behind the crime.
Could a possible murderer lie in its pages, with a personal connection to Darlene Ferrin.
To examine this topic on the Blue Rock Springs Attack, that resulted in Darlene Ferrin becoming the third victim to fall at the hands of the infamous Zodiac Killer please visit this link at ZodiacKillerNet.