The notion of an author spending a considerable amount of time choosing this particular card, methodically finding and pasting particular text from newspaper cuttings onto the card, and then punching a hole into a preselected position, to then get the victim total horribly out of sequence, doesn't hold any water. Anybody prepared to go to these lengths to design a postcard, to then be accused of failing to notice the innumerable newspaper articles featuring the Zodiac Killer claiming 12, 13, 14 and 17 victims, simply doesn't stack up. Not withstanding the fact, that the author wasn't claiming 12 victims, because he used the past participle of seek (in sought), thereby taking us back to an earlier time.
The Zodiac Killer wasn't responsible for the disappearance and murder of Donna Lass, however, this cleverly designed and thought out card was created to give the impression he was, by suggesting he had trailed her from state to state and wasn't to be denied. Just four months later he would use exactly the same technique when designing the pasted Monticello card. He again retrospectively claimed the murder of Kathy Bilek on July 13th 1971 when this card was mailed. Kathy Bilek was murdered three months earlier in the Villa Montalvo woods in Saratoga on April 11th 1971 - and hence why the Zodiac Killer used the past tense of "shought victim 21" one again. He was taking us back to an earlier time and claiming he had trailed Kathy Bilek before murdering her. We know he wasn't responsible for the murder of Kathy Bilek (because Karl Francis Werner was ultimately jailed for the crime), and so he was very likely not responsible for the Donna Lass murder either. In both cases he attempted to bamboozle us with cryptic text, to deflect from the reality that he had nothing to do with either crime.
The Monticello card, just like the Pines card, contained a set of directional instructions which revealed a name - and both led to a Memorial Park. This level of ingenuity and thought, not the hallmarks of a casual hoaxer. The Monticello card was the culmination of a deception spanning nearly two years, but as of August 31st 2020 it has never been released into the public domain.