This can be seen on November 9th 1969, when the Zodiac Killer highlighted one particular section of his letter, stating "p.s. 2 cops pulled a goof abot 3 min after I left the cab. I was walking down the hill to the park when this cop car pulled up + one of them called me over + asked if I saw anyone acting suspicious or strange in the last 5 to 10 min + I said yes there was this man who was runnig by waveing a gun & the cops peeled rubber + went around the corner as I directed them + I disappeared into the park a block + a half away never to be seen again". The Zodiac Killer did this by placing arrows across this section of text with the accompanying phrase "Must print in paper". His knowledge of the police at this particular location was his proof of being there. However, there is one crucial thing missing from the red section of text above. It should have read "I said yes there was this black man who was runnig by waveing a gun".
But how do we know that Officer Donald Fouke didn't include the "black male" description when talking to Zodiac? Because the Zodiac Killer would have written "have you seen a black man acting suspicious or strange in the last 5 to 10 min" in his November 9th 1969 letter as further proof he spoke to officers, had Donald Fouke said such a thing. Why on earth would the Zodiac Killer omit such a crucial detail like this from a section of text he made a point of highlighting? Probably because Officer Donald Fouke wasn't looking for a black male on October 11th 1969, having never been given this instruction by the dispatcher. It was likely a fabrication issued to him by his superiors, to be documented in a memorandum on November 12th 1969.