It was likely the newspaper coverage of the Park Station bombing that inspired his following two communications. The Dragon card mailed 8 days later, carried the introduction of "If you dont want me to have this blast you must do two things. Tell everyone about the bus bomb with all the details. I would like to see some nice Zodiac buttons wandering about town. Everyone else has these buttons like, black power, melvin eats bluber, etc". The bombing at Park Station was believed early on to be the work of the Weather Underground or the Black Liberation Army, hence the Zodiac Killer's need to get some recognition by the requesting the wearing of Zodiac buttons and referencing Black Power. It may also be significant that he placed "I hope you enjoy yourselves when I have my Blast" right alongside a picture of Don Quixote and Sancho Panza, suggestive of a location. A statue of Miguel de Cervantes, Don Quixote and Sancho Panza can be found in Golden Gate Park in San Francisco, approximately one mile from Park Station (1899 Waller Street), which also sits in Golden Gate Park, in the southeast corner. This threat of a blast, in accompaniment to the imagery, indicative of a compassionless killer piggybacking upon the Park Station bombing, by suggesting a threat in the near vicinity. An ominous foreboding that was already embedded in the April 20th 1970 letter in the form of the school bus bomb diagram. Just two months later, on June 26th 1970, the Zodiac Killer would expand on his bus bomb diagram by supplying us with extra details.
A bomb placed on the embankment of the Southern Freeway (274 feet from Ingleside Police Station) is notable for another reason. The Zodiac Killer didn't state he would "annihilate a school bus" on June 26th 1970, he promised to "annihilate a full school bus", suggesting that the school bus would have to be near the terminus of its route. The Thomas More Catholic School had a bus route along the Southern Freeway, just yards from Ingleside Police Station, passing a location mimicking the bus bomb diagram (shown below in red), with the school itself situated in the southwest corner of San Francisco. Children traveling from all over San Francisco would have been seated on this bus as it drove south in the morning light. The sun would have been to the east, with the school bus exiting the freeway extremely close to the school. It most certainly would have been full as it passed the proposed bomb location.
The Zodiac Killer threatened to kill police and place bombs, but he will be ultimately remembered for targeting the young and defenceless - and just like most serial killers - be recognized for the coward he was.