Zodiac killer

Clues To A Planted Bomb

Also included was a map of the Bay area. A clock-like face had been drawn around Mount Diablo with a zero at the top, the number three on the right side, six on the bottom, and a nine on the left side. Next to the zero, he wrote, "is to be set to Mag.N."

The map and the cipher were supposed to give the location of a bomb the Zodiac had buried, set to go off the following fall.

This letter was signed "[Zodiac Symbol]=12. SFPD=0."

The next month, in another letter sent to the Chronicle, the Zodiac took credit for abducting Jones four months earlier and described burning the car, a fact that only one local paper, The Modesto Bee, had printed.

In another letter received two days later, the Zodiac included a twisted version of the song "I've Got a Little List" from Gilbert and Sullivan's operetta "The Mikado," describing how he planned to collect and torture his slaves. Also drawn on the letter was a giant crossed-circle, a score notation of "=13, SFPD=," and the words:

"PS. The Mount Diablo Code concerns Radians + # inches along the radians."

In 1981, Zodiac researcher Gareth Penn figured out that when placing a radian, or angle measurement, over the map, it pointed to two locations where the Zodiac attacks took place.

Three months passed with no communication from the Zodiac. Then, on October 5, a card made of letters cut from magazines and newspapers was sent to the Chronicle. 

The card, which bore 13 holes, indicated that there had been another Zodiac victim and that he considered himself "crackproof." 

Originally considered a hoax, certain letter configurations and the phrase "crackproof" later reappeared in confirmed Zodiac letters, adding authenticity to this one.