The Button Letter was mailed to the San Francisco Chronicle on June 26th 1970, accompanied by a map of San Francisco and its vicinity. On the map, the Zodiac Killer had added his traditional crossed circle centered over Mount Diablo, however, on this occasion he added the numbers 0,3,6 and 9 around its circumference, or more specifically, on the cardinal points. Crucially though, he also added a directional marker on the North facing compass point as a positional indicator.
It is believed, along with the inserted code, to possibly indicate the location of a hidden bomb buried by the Zodiac Killer. However, Kevin Robert Brooks is convinced he has unearthed the true reason behind the killer's motive for the design of the Phillips 66 Petroleum Map, and the answer lies a little closer to his suspect's home.
In many Zodiac communications, the Bay Area killer repeatedly taunted police and newspapers alike, promising to reveal his name, although in all likelihood this was never a realistic hope. But it just may be, that despite his reluctance to offer us his name, he quite possibly offered us the next best thing - his residence or place of birth.
Donald Lee Bujok was born on July 6th 1936 in Roundup, Musselshell County, Montana, and Kevin Robert Brooks believes this crossed circle may indicate the county seat of Roundup, albeit in an extremely subtle way.
On the Phillips 66 Petroleum Map, the Zodiac Killer added a notation that his design "is to be set to Mag.N". Taken to be Magnetic North.
In 1970, Magnetic North was approximately 16.5 degrees.
If we adjust the crossed circle accordingly by 16.5 degrees, it becomes even more significant, with the directional marker passing exactly over both county seats of Winnett and Malta, shown on the map to the left.
Most of this was addressed in the Phillip Petroleum Map Key article on December 26th 2013, however, there is just a little bit more.
The county code numbers of Petroleum County and Phillips County are 55 and 11 respectively. These totaled up equal 66, to provide yet another interesting feature, bearing in mind the Phillips 66 Map.
Thanks again to Kevin Robert Brooks.