Profile
Police profilers considered the Zodiac killer an "extremely shrewd, methodical planner" who would have had knowledge of cryptography, guns, map reading, meteorology, astronomy, drafting, and a probable military background. [32]

Self described as the son of an Army cryptographer and former employee of the California Attorney General’s office, Penn has written that he had a "checkered career" as a “medievalist, artillery surveyor, free lance writer, economic researcher, reference librarian, and receptionist in a robot factory.” [33]

In Times 17 Penn writes that he received artillery training at Fort Sill, Oklahoma during the mid-1960's. A U.S. Army artillery surveyor performs astronomical observations; measures azimuths, grid coordinates, and angles on maps; and operates/maintains vehicles, radios, weapons, and other survey equipment in support of artillery operations. [34]

Amateur investigators have noted that in Times 17, Penn audaciouly lays out a scenario whereby, as duty person in charge of daily roll call, he could have falsified an entry and left Fort Sill in October, 1966, taken a military hop to March AFB, and killed Cheri Jo Bates in nearby Riverside. [35] [36]

Based on his dates of service, Penn would have served during the Vietnam War.[37]

[edit] Writing style
A prolific letter-to-the-editor writer, Zodiac used British phrasing that incorporated numerous references to theatrical, literary, or linguistic works.

Recurring Zodiac themes included Gilbert and Sullivan’s Mikado; Old Norse limericks and poetry; epigrams, acrostics, and cryptograms; and high-handed word play intended to baffle and belittle the authorities.

Gareth Penn’s proclivity toward astute, officious, and often biting letters to the editors of the world’s top intellectual periodicals -- such as Scientific American, Nature, The Economist, and at least 15 letters over the years to National Public Radio -- has tantalized amateur sleuths as another similarity between Penn and Zodiac [42]

In an Ecphorizer article entitled Lima Riki, Penn notes that "in a previous incarnation," he used to write limericks "in Old Norse." A Zodiac letter mentions Old Norse writing, an issue Penn subsequently addressed.[43] [44] [45]

The author's efforts to implicate his suspect continued in the years since the publication of ZODIAC. Graysmith spread an unsubstantiated rumor that Allen had received a speeding ticket near the scene of Zodiac's Lake Berryessa attack. This rumor eventually appeared as a verified fact in a book written by former FBI profiler John Douglas.

Graysmith claims in one quick sentence, "Sherwood Morrill confirmed my theory." (pg. 219). Yet he states that in 1981 he "dropped in on Sherwood Morrill "to compare handwriting of a suspect with the Zodiac's (Zodiac, pg. 298, paperback edition). If Morrill actually believed that Graysmith's projector theory was true, he would not continue to exclude or include suspects based on their handwriting. Graysmith seems oblivious to this blatant contradiction.

Official documents and media interviews, as well as the expert's family, demonstrate that Morrill's opinions never changed throughout his many years on the case. Until his death, Morrill stated that he was certain the Zodiac used his normal handwriting when writing the letters and the expert was unwavering in his belief that he could identify the killer using little more than a bank deposit slip.

Graysmith also attempted to revise Vallejo geography on page 425 of Zodiac Unmasked. The author claimed to have discovered a "hidden road" that led him "in a dead straight line" from the crime scenes to Allen's home. Graysmith claimed the road was so well hidden that he had to make an "abrupt turn" to make this sensational discovery.

In June of 2003, several Zodiac researchers drove the streets of Vallejo in an attempt to locate the road Graysmith described but were unable to do so using the information provided in the book. Telephone requests for assistance from the author went unanswered. Further research proved that Graysmith's phantom road does not appear on maps from the 1960s or today, and, in fact, never existed.

On page 200 of Zodiac Unmasked, Graysmith presents a drawing he claims Karen Allen produced while under hypnosis using "automatic writing." The drawing allegedly proves that Allen was in possession of Zodiac-like codes long before the killer's codes appeared in the newspapers. Karen Allen was never hypnotized, and she never produced the drawing shown in Graysmith's book.