The threat of killing "a family of five between now and Monday" is rather specific, almost as though he had earmarked a couple with three children. We know the Zodiac Killer read the August 4th 1969 San Francisco Examiner and August 6th 1969 San Francisco Chronicle newspapers, which may have inspired his attack at Lake Berryessa and certain subsequent claim to the Snoozy and Furlong murders by the addition of "Aug" on the November 8th 1969 Dripping Pen card. This was an obsession he would carry forward into 1971, referencing the Snoozy and Furlong murders at least two more times, if not three.
The August 6th 1969 San Francisco Chronicle article, entitled The Frenzy Of San Jose Girls Slayer, read under the banner of Children "The other Furlong children are Glen, 16; Floyd, 12, and Pamela, 11. Furlong said he did not know and had not yet talked to Kathy's parents, Mr. and Mrs. Wilfred Snoozy. Both Snoozy, a carpet layer, and Mrs. Snoozy reportedly are in a state of collapse. Her funeral has been scheduled Friday at 11 a.m. at the Place Funeral Home in Los Gatos. Burial will be at Oak Wood Cemetery in Santa Cruz. Funeral services for Kathy will be held tomorrow (Thursday) at 2 p.m. at the Oak Hill Memorial Park Mortuary in San Jose. Burial will be at Oak Hill Memorial Park". The Furlong's had three surviving children called Glen, 16; Floyd, 12, and Pamela, 11, which ties in with the threat from the December 19th 1969 telephone caller to kill "a family of five between now and Monday".
THE ZODIAC KILLER PHONE CALLS TO BARSTOW [PART ONE]
Thanks to Jibberjabber for his assistance in this matter.