The solution to what’s known as the 340 Cipher, one of the most vexing mysteries of the Zodiac Killer’s murderous saga, has been found by a code-breaking team from the United States, Australia and Belgium. The cipher, sent in a letter to The Chronicle in November 1969, has been puzzling authorities and amateur sleuths since it arrived 51 years ago. Investigators hoped the Zodiac, who killed five people in the Bay Area in 1968 and 1969, would reveal his name in one of his many ciphers, but there is no such name in the 340. According to code-breaking expert David...