It seems a strange timeline the Zodiac presented us with, in that his first confirmed murders were that of David Faraday and Betty Lou Jensen at Lake Herman Road on December 20th 1968, after which nearly seven months would pass before the Blue Rock Springs attack, which started a period of three crimes in a little over three months, then nothing. However, his letter writing went unabated until March 22nd 1971, if you believe the Pines card to be genuine Zodiac correspondence, before he disappeared for nearly three years, until the arrival of the Exorcist letter on January 29th 1974. However, his murders and correspondence both followed a pattern for three consecutive years.
After the first confirmed murders at Lake Herman Road on December 20th 1968, the Zodiac Killer reappeared on July 4th 1969, a gap of 197 days. At the end of 1969 he mailed us the Melvin Belli letter on the anniversary of the Lake Herman Road double murder, but would again go into winter hibernation from December 20th 1969 until the arrival of the 'My Name is....Letter' on April 20th 1970, a gap of 122 days. This excludes the disputed Modesto abduction of Kathleen Johns on March 22nd 1970 - but even if it was included, the difference would still amount to 93 days. Finally, the end of 1970 would again see the Zodiac Killer disappear beyond the radar, from his mailing of the Halloween card on October 27th 1970 to the Los Angeles letter on March 13th 1971, a gap of 138 days. Three consecutive years with periods of hibernation spanning 197,122 and 138 days, averaging out at 152 days or 5 months of silence - yet on every other occasion the time delay between contact is less than a month. Is this coincidence, and if not, where did he go during these periods of inactivity? Did he take his crimes out of state, did he visit family or did a particular profession negate his ability for contact.
Carl Feigenbaum may have taken the opportunity as a visiting sailor to commit crimes beyond his natural habitat - an opportunist who murdered five women on the streets of Whitechapel beginning with Mary Ann Nichols on August 31st 1888 and ending with Mary Jane Kelly on November 9th 1888, all told, in a little over two months and then he vanished.
The Zodiac Killer also committed five confirmed murders in a little under ten months, ending with the murder of Paul Stine on October 11th 1969 in Presidio Heights, however, it would be another five years before the last traces of the Zodiac Killer would be heard from again.