In light of the bizarre letters to area newspapers that followed the Bates murder, it is no surprise that the Bay Area killer was later considered a likely suspect for that attack.  This theory, however, was almost immediately discounted by detectives in Riverside, who had a suspect of their own: a jilted boyfriend who was jealous of Bates' relationship with another man.  Indeed, the specifics of Bates' murder did not resemble the Zodiac's MO at all: while the Zodiac struck almost invariably at couples he found while cruising isolated areas, there was no such opportunism in the attack on the RCC coed.  Rather, her killer appeared to have targeted her specifically, sabotaging her car while she visited the library and then lying in wait for her to return.  While the Zodiac eschewed personal contact with his victims (except in one instance when they were physically restrained and his identity was concealed behind a hood), Bates' killer spent over an hour with her in the dark but urban environs of RCC's library annex.  Where the Zodiac was careful to maintain situational control through tactics and weaponry, Bates' killer seemed both surprised by his victim's resistance and inappropriately armed, using what was probably a small pocketknife to kill her.  If this had been the basis for comparison between the Riverside attack and those in the Bay Area, there likely would never have been an attempt to link the two.

The Bates case did not end there, however.   Two sets of anonymous letters were sent in Riverside following the murder. The first set, containing copies of the "Confession" letter, was sent on November 30, 1966 to the Riverside Police Homicide Detail and the Riverside Enterprise .  The envelopes were unstamped and the addresses were incomplete: the copy sent to the RPD was addressed simply to "Homicide Detail, Riverside," while the newspaper's copy was addressed to "Daily Enterprise, Riverside Calif, Attn: Crime."  Later this year or early the next, a poem  that appeared to descibe the murder was found scratched into a desk at the RCC library.  The second mailing, composed of the handwritten "Bates had to die" notes, was sent in April 1967 to the Riverside Police Department, the Riverside Press-Enterprise, and the victim's father, Joseph Bates.  These envelopes were sent with extra postage and the correct street addresses, except for the RPD's copy, whose address was given as "Riverside, Calif."  The envelopes can be seen here.

Although the Riverside communications -- the "Confession" letters, the poem, and the "Bates" notes -- are often considered to be the handiwork of a single person, this theory is in fact open to debate.  Following the Avery series, a November 1970 examination by  Sherwood Morrill, the state's Chief Examiner of Questioned Documents, indicated that the author known as the Zodiac had written the poem as well as the "Bates Had to Die" notes, but no such finding was made on the typed "Confession" letters' envelopes, and these were the only Riverside communications that indicated any direct knowledge of the crimes.  Moreover, though the Riverside Daily Enterprise and the Riverside Press had been under joint ownership since 1932, they were two different newspapers: the Enterprise was a morning paper that circulated in Riverside County outside city limits, while the Press was an afternoon local that served the city.  The Press-Enterprise was the corporate name of the publisher, and would not become a newspaper in its own right until 1983, but the title would have appeared in the newspaper's indicia along with its address.  Joseph Bates' address had also appeared in one of the articles on Bates' murder, suggesting that the author of the "Bates" notes had gleaned the addresses from the paper while the "Confession" author had not performed such research and simply trusted in the local post office to find the street address.  Given the very different nature of the two sets of letters, the different newspaper titles to which they were addressed, and the absence of a link through handwriting analysis, the possibility that they were composed by different authors becomes significant.

Found at the scene of the crime were a men's Timex wristwatch, about ten feet from the body; a heelprint from a military shoe; freshly-gouged dirt indicating a terrible struggle, and several fragments of hair and skin in Bates' hand and beneath her fingernails.  The wristwatch in question was fitted with a band that measured just 7 inches around -- it was a men's model,  but the circumference of the band was of a size often used by women and young or narrow-wristed men.  Since it was never identified as the victim's by her father or by investigators, the most likely explanation for its presence so close to the victim's body is that it was torn from her attacker's wrist as the two grappled, though this can not be stated with absolute certainty.  The heelprint was from a common military model available at a local Air Force base, and came from a shoe between sizes 8 and 10, again indicating an assailant with a small to medium frame.  Bates weighed just 110 lbs when she was killed, and while even a woman of slight build can put up a significant fight under life-and-death conditions, the inability of her attacker to easily dominate her is another indicator that he was not particularly large or strong.  Finally, the location of the crime, a college campus, is a place where such a man -- young, disorganized, and emotionally attached to his victim -- might be found.

All of these factors are in contradiction to the evidence and descriptions we have in the Zodiac murders.  The footprints found at the Lake Berryessa crime scene were from a size 10.5 shoe, half a size larger than the largest estimation of the Riverside print.  Though they aren't known to be the Zodiac's, the pair of men's gloves found in Paul Stine's cab were size extra-large, indicating large hands and, presumably, large wrists as well.  Witnesses consistently described the Bay Area killer as larger or heavier than average, not slim or even medium-sized.  The Zodiac seemed entirely prepared for his murders, knowing before he even arrived at the scene what he would do and how he would do it.  Never did this entail stalking, targeting, or the sort of conversation that probably passed between Bates and her killer.  Finally, the Zodiac displayed a propensity to claim unrelated murders as his own work, particularly from 1970 onward; it would not have been out of character for him to claim the Bates murder in those latter days, and the incidents in Riverside may even have inspired his letter-writing campaign to begin with.  Regardless of whether Bates' killer was the man suspected by police, the evidence at hand does not point to the Zodiac as the assailant.