My understanding is the police used fellow colleagues to see who could make a similar impression and then recorded his weight.
I doubt they lied about performing such an obvious and empirical test, if this is what was said to have happened.
So if the police were able to leave impressions for the purpose of their test, the Zodiac was likely able to leave impressions earlier.
Also, it was into winter and much later at night when Jensen and Faraday were killed. Contrarily, at LB, the day was much warmer, warm enough for Hartnell and Shepard to not wear bulky clothing, or light coats even, warm enough for Fong to fish, and warm enough for three young women to sunbath in their bikinis near the lake.
(All of this was pretty much mentioned above in one for another. Just wanted to further clarify)
As for the ground being "baked and dried"...that depends on a variety of factors such as humidity, soil composition, et cetera.
I get what is being said about how the prints could have originated days earlier, but one has to imagine the cops could tell the difference between "baked" and thus old prints, and those that were laid recently. I could. You probably could too. Doesn't take a Sherlock for that one.
That and as I said, IIRC, the police performed the aforementioned basic test, which if true means then that the relevant ground area was not baked hard. Again, many factors contribute to a lack of shoe impressions at an outdoor crime scene.
Finally, from the image: ground looks granular to me, and thus not only capable of recording a print but also capable of being further atomized by weight, which means the Zodiac would have been able to leave an impression. Also: apparently his car left tire impressions on what appears to be a dirt road. If the car could leave impressions, it's not a stretch a 220+ pound man was able to do so either. I'd imagine the road would be much more hard-packed given its parallel nature to the sun's rays and the fact it was far more well-traveled than the area the Zodiac traversed.
http://www.zodiackiller.com/WWPrint1.htmlhttp://www.zodiackiller.com/TireTracks.htmlEDIT: Police report says one such shoe impression, bearing the "suspected tread pattern". was found in SAND:
http://www.zodiackiller.com/LBReport17.html[Robert_Graysmith]_Zodiac(BookZZ.jpg
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