
One would presume the only person who knew that Leona Roberts wasn't going to be killed immediately after being abducted was the killer, which is why the two "forecast" letters on December 10th 1969 and December 11th 1969 are extremely interesting. The two pasted horoscope communications entitled Day-By-Day Forecast For Cancer and Day-By-Day Forecast For Leo, bearing in mind the latter could easily be interpreted as Day-By-Day Forecast For Leona Roberts, is extremely perintinent when we consider the timing of the communications and her abduction. The December 10th communication also came with the pasted pseudonym of "ZODIAC" emblazoned across its face. The fact that these communications were a forecast (a prediction of what will happen), coupled with a Zodiac horoscope and the distinct possibility that "Leo" was chosen for purpose, then the discovery of her body eighteen days later at Bolinas Lagoon in Marin County, is rather curious.
The coroner concluded that she had likely been dead "4 to 7 days prior to recovery, and he theorized that she had been alive 10-14 days after her abduction". She was abducted on Wednesday December 10th 1969 and found at Bolinas Lagoon on December 28th 1969, so that places her murder between December 20th 1969 and December 24th 1969, allowing for a small margin of error. The longer between death and discovery, the more difficult it is to make an accurate determination.
The coroner concluded that she had likely been dead "4 to 7 days prior to recovery, and he theorized that she had been alive 10-14 days after her abduction". She was abducted on Wednesday December 10th 1969 and found at Bolinas Lagoon on December 28th 1969, so that places her murder between December 20th 1969 and December 24th 1969, allowing for a small margin of error. The longer between death and discovery, the more difficult it is to make an accurate determination.

The Zodiac Killer mailed the Fairfield letter on December 16th 1969, but he made no update to his running total of seven victims. In this communication he added a supplemental drawing of a "Bleeding Knife" with seven drops of blood, possibly fashioned to incorporate the two extra victims he was claiming, that of Kathy Snoozy and Deborah Furlong murdered in San Jose on August 3rd 1969, by knife. Just four days later, the Melvin Belli letter arrived at the San Francisco Chronicle stating the Zodiac Killer was resisting the temptation to murder his ninth and tenth victim. This appears to indicate that victim number eight was secured between December 16th 1969 and December 20th 1969, which falls around the approximate time the corner determined that Leona Roberts was murdered. If the above interpretation is correct, we would have three Zodiac communications on December 11th 1969, December 16th 1969 and December 20th 1969, giving us a "forecast for Leo", a failure to update the running victim total five days later, followed by an update to eight victims just four days later, around the time Leona Roberts was killed.
The phrases on the Cancer and Leo communications are difficult to interpret, but when we consider the random phrase of "BIRDS FLY SOUTH" (pasted between the 18th and 24th) and the location where her body was discovered, on a north to south Pacific Flyway for migratory birds, one can't help thinking that the pasted clues were cryptic in nature. Further investigation "determined that a unique wristwatch was missing from the girl's wrist, but a Napa High School class ring given to her by a neighbor still remained on her finger", thereby making the prominent "WATCH" on the face of the Cancer communication another noteworthy addition. Irrespective of their correct meanings or otherwise, the "forecast" letters and the timing of Leona Roberts abduction should not be overlooked. It is likely only one person knew the day-by-day forecast for Leona Roberts, and his identity remains a mystery to this day.
The phrases on the Cancer and Leo communications are difficult to interpret, but when we consider the random phrase of "BIRDS FLY SOUTH" (pasted between the 18th and 24th) and the location where her body was discovered, on a north to south Pacific Flyway for migratory birds, one can't help thinking that the pasted clues were cryptic in nature. Further investigation "determined that a unique wristwatch was missing from the girl's wrist, but a Napa High School class ring given to her by a neighbor still remained on her finger", thereby making the prominent "WATCH" on the face of the Cancer communication another noteworthy addition. Irrespective of their correct meanings or otherwise, the "forecast" letters and the timing of Leona Roberts abduction should not be overlooked. It is likely only one person knew the day-by-day forecast for Leona Roberts, and his identity remains a mystery to this day.