The letter was effectively a mishmash of previous Zodiac tropes, but significantly, it mimicked his first ever letters to the San Francisco Chronicle, San Francisco Examiner and Vallejo Times-Herald on July 31st 1969. These 1969 letters threatened to go on a "kill rampage" over the weekend if his ciphers were not published on the front page of the respective newspapers. The Exorcist letter mailed on January 29th 1974 was identical, threatening that if his note was not published in the paper he would do something nasty which you knew he was capable of doing. The only thing synonymous with the Zodiac Killer that we knew he was capable of doing, was "to kill". This logically should be the conclusion. Therefore, it makes perfect sense, that the strange collection of characters at the foot of the Exorcist letter should be able to be rearranged to the spell the verb "to kill". This is exactly what Kevin Robert Brooks, author of the upcoming book The Montana Connection, discovered several years ago - and it is the logical extension to the passage above it. Whether or not the Exorcist letter was written by the Zodiac Killer is another matter entirely.
The S.L.A. communication finished off the message by highlighting the word "kill", exactly as the Exorcist letter had done just 5 days earlier. Furthermore, the S.L.A. letter began its introduction with "Dear" and signed off with "a friend". This is important, because 7 days later the real Symbionese Liberation Army mailed a letter to the Hearst family on February 10th 1974, beginning their correspondence with "Dear" and ending the communication with "A friend". Uncanny that.
So, did the Zodiac Killer reappear from his slumber after nearly three years to critique the Exorcist film for our benefit, and tell us that "sla" (Symbionese Liberation Army) was the Old Norse word for "kill" to expand our foreign language skills? - which in all likelihood is the dominant hidden word in the Exorcist letter. Or, is it more likely the Symbionese Liberation Army wrote the February 3rd 1974 S.L.A. letter one day before the kidnapping of Patricia Campbell Hearst by the S.L.A, and referenced the Symbionese Liberation Army within their own communication? Then just happened to mail another letter only 7 days later writing "Dear" and "A friend", exactly mimicking their previous one. To some, the Exorcist Letter is beyond reproach, so I guess the.legend lives on.