Leona Roberts was abducted on December 10th 1969, in tandem with a communication of pasted words that contained "Zodiac", "Watch" and "Birds Fly South". This communication, eighteen days in advance of her body being discovered, highlighted the word "Watch" in the largest letters, and significant bearing in mind a unique wristwatch was reported missing from the girl's wrist on December 28th 1969. She was also found at Bolinas Lagoon, so the "Birds Fly South" phrase may have some meaning when we consider that Bolinas Lagoon is a major north-south Pacific flyway for migratory birds in America, extending from Alaska to Patagonia.
The Zodiac Killer had claimed seven victims on November 9th 1969, but he didn't (assuming it was Zodiac) raise this victim count in the two forecast letters on December 10/11. He also made no change to his victim count in the two Fairfield letters mailed on December 7th and 16th. Yet he did raise his victim count to 8 on December 20th 1969, when he stated "I am afraid I will loose control again and take my nineth & possibly tenth victom". This could imply the Zodiac Killer claimed his eighth victim between December 16th and December 20th 1969 - very close to the estimated time of death of Leona Roberts. The estimation of death with increased time is obviously more difficult to pinpoint, so it's perfectly feasible an error of just one or two days, places her time of death between the period Zodiac's victim count increased to eight. The two forecast letters were never publicly released, making the threatening "Zodiac" phone call to Peggy Trainer (18) on January 4th 1970, who lived behind the apartment where Leona Roberts was abducted, a further uncanny coincidence.