Okay, so I’m sure most Zodiac investigation veterans (probably the majority of this site) will find this thread silly. After all, they’re already experts on the case, so what need do they have of this thread? But for those that are new to the case, are beginning their own investigation into a POI, or are like me and like to amass their information into one organized place, this hopefully will prove to be an asset. I hope no one finds this thread "needless" and ends up getting locked and deleted.

This is going to be a collection of Zodiac information and theories. Note that I do not claim to necessarily believe what is said here, but I also do not think that I am in a position to say someone’s theory is incorrect, especially considering how much noise and confusion there is surrounding this case. I present each within an organized section, briefly describe it, and possibly add my own thoughts at the end in italics. Sometimes it helps to consider alternate paths. This is sort of like a collection of "what ifs".

At the moment this is not an exhaustive compilation, especially in regards to suspects. I will update this more over time.

Zodiac’s Motive (Why did he kill?)
*To collect slaves for the afterlife. He truly believed this concept, that in killing people they would be his slaves in "paradice". It’s possible that if this were truly a motive for him, that this may indicate a mental instability, although there are old religious connections to the premise.

*He wanted attention. Not only that, he wanted people to be talking about him. He wanted to be in newspapers and on television. This likely indicates a very lonely person. This could also simply be someone with a chronic need to be the center of attention, and perhaps he wasn’t getting it. This person could also perhaps have had delusions of grandeur and their daily life did not live up to what they felt they deserved. He enjoyed having people talk about him, particularly law enforcement. Obviously the need for attention was true for the Zodiac, or else he would not have written all of the letters.

*Revenge. The Zodiac knew his victims and that is why they were murdered. They crossed him somehow and in his mind, they deserved to die for it. Other victims may have simply found out his secret.

*Rejection from a love interest. The Zodiac largely targeted couples, and women were attacked more brutally. He either murdered girls he wanted who rejected him, or girls that reminded him of the girl who did. Or possibly both. This is not mutually exclusive with the above, "Revenge". Other victims may have simply found out his secret.

*Terrorism. He enjoyed striking fear into peoples’ lives. He outsmarted the police, so what hope did his next potential victim have? He was always looming, ready to strike again at any time.

*He enjoyed it. This obviously is not mutually exclusive to any other motive. He can still have other reasons pushing him towards killing and also enjoy it, of course. His need to kill came simply from his desire to do so. It was better than "getting your rocks off with a girl". This could also possibly have been his sole motivator. What better reason is there to do something than for enjoyment? This indicates someone with a lack of morals; a psychopath.

*He didn’t enjoy killing. The murders were simply a means to an end: fame.

Zodiac’s Letters
*He wrote all Zodiac letters. This includes the ones thought to be fake. He changed his handwriting just to see if law enforcement were up to the task of figuring out it was him, which they failed at. This ideas is very unlikely, at least as far as being able to change your handwriting enough to convince an expert.

*He wrote all confirmed letters. Other than the known forgeries, Zodiac wrote and mailed all suspected letters.

*He wrote none of the letters. Every letter has been a fake. Very unlikely considering the letters that contained a piece of Stine’s shirt.

*He wrote some letters, or "authorized" them. The Zodiac didn’t work alone. He did the killings and one or more people authored the letters, possible including the ones thought to be fake as part of "Team Zodiac".

*There are more letters from Zodiac that we don’t know about yet. Law enforcement didn’t want to give up information that would potentially harm their case, so they held back from informing the public of other Zodiac letters. Incidentally, this is true! There is the infamous "DMV Letter", which I am unsure of whether or not has made its way online yet, as well as – my source tells me – 2 more confirmed letters and another one inconclusive. From what I understand, they contain the names of still living people.

*The handwriting in the letters is Zodiac’s true handwriting. Changing your handwriting significantly enough to fool an analyst is a near-impossible task. He wrote the same way in his letters as he did in his everyday-life. Zodiac was confident he wouldn’t be caught and so no reason to bother even trying to mask his handwriting.

*The handwriting in the letters is not Zodiac’s true handwriting. Assuming the handwriting is even his, it’s not the way he normally wrote. He either changed it enough to fool experts, or under the influence of drugs, a mental condition, or a combination, his handwriting changed enough to become distinctly different than his own. Serial killers are also known to act very differently during the time preceding and sometimes even after a murder than they do in the rest of their life. It’s possible this "duress" he was under for his need to kill altered his handwriting as well. To me, this scenario seems very unlikely in every way. Whether or not he consumed drugs, or had a mental condition, it is VERY unlikely to fake handwriting that well to fool experts, even in the 70s. That does not mean it’s impossible, however.

*The signature in The Exorcist letter is a bodycount. The Zodiac has been keeping score and is informing us he’s been busy, having killed a total of 37 people.

*The signature in The Exorcist letter is not a bodycount. He is either trying to indicate something other than his number of victims, or he is trying to obfuscate the investigation. Normally he signs with he circle cross symbol, but this time he specifically signed it "Me". A popular theory is that he’s giving his age – but that doesn’t fully explain the "SFPD – 0" beneath it, if true. Still…

Zodiac’s Unconfirmed Victims + Victim Total
I will not go over reasons as to why these victims are possibly associated with Zodiac, as that is beyond the scope of this thread.

*Robert Domingos & Linda Edwards – 6/4/63

*Cheri Jo Bates – 10/30/66

*Kathleen Johns – 3/22/70 – "victim" does not necessarily mean one who was murdered, keep that in mind!

*Donna Lass – 9/6/70

*Zodiac only had the 7 confirmed victims. He simply tried to take credit for others and his hints that there were more were just him trying to sow confusion among law enforcement, at which he succeeded.

*Zodiac’s victims included the other 5 commonly attributed to him, bringing them up to 12 (9 murdered). There is strong evidence connecting him to the above cases. The only reason they’re unconfirmed is because he never provided proof like he did for his other victims.

*Zodiac killed 37 people. In the Exorcist letter, Zodiac signs it "Me – 37" indicating his kill count.

*Zodiac has killed more than 37 people.. He’s a killing machine. He no longer felt the need to brag endlessly to police and newspapers about his exploits, he just kept killing.

*Zodiac never killed anyone, or at least no one he claims to have.. It’s all a "hoax". There is no Zodiac serial killer. These killings are all unconnected, and someone has been perpetuating the lie that there is one killer eluding law enforcement all these years.

Zodiac’s Identity
I will expand upon this section over time

*Arthur Leigh Allen – LOL. Er… sorry. I know, I know, I said I would remain impartial, so here we go. Favorite suspect of Graysmith, to the point of fabricating witness stories and information to shoehorn him into the role of Zodiac. But no, it is still possible. Pretty much anything is possible in this case at this point, within reason. Allen was certainly an unsavory person, to say the least, and it’s no surprise that he became a suspect in the case. A common theory amongst investigators supporting the idea of Allen as Zodiac is that while he committed the murders, he had a friend write the letters, which is why his handwriting was not a match. In fact, Vallejo Police Department even operated under this theory in the 90s (I am unsure if they still feel this way).

*Fred Manalli – In many ways, Manalli fits well into the role of Zodiac suspect. Most notable is his handwriting, which is an incredible match to Zodiac’s. There is also the fact that the day after Manalli died, the infamous ad in the newspaper stating "Zodiac, your partner is in deep real estate" ran, which, in this scenario, would seem to indicate not only a "Team Zodiac" but that Manalli was in some way part of it, likely as the one who wrote the letters.

*Richard Gaikowski –

*Lawrence Kane –

*Ted Kaczynski – The Unabomber. Surprisingly at first, Ted actually is a good candidate for Zodiac. His handwriting is a very good match to Zodiac’s. He is known for mailing bombs to people, but he is also known to have committed other violent crimes and indicating in journals wanting to murder boisterous couples in love. There are also several items he owned in his cabin that connect to the Zodiac case, including the same brand of ammo. His cabin was also located in Deer Lodge Kaczynski is still alive and in prison, but the fact that he has denied being Zodiac is not enough reason to rule him out. Before being caught he meticulously took notes and wrote everything down in journals. However he destroyed much of it, particularly from the time the Zodiac was known to be active. He is commonly looked upon as a hero in radical activist groups, and he is aware of this fact. Admitting to the world that you were also a serial killer in the 60s and 70s would kind of tarnish that image for him. There is also an abundance of other, often minor, facts linking him to the Zodiac. Kaczynski as Zodiac supporters also like to point out the similar lexicon of the two. Personally, however, most of that is coincidental and sometimes really stretching. I understand that it’s "not only did they use the same words and phrases, but they did it repeatedly and numerously" but to those that think that: that is really not as unusual as you make it out to be. However, he is still a favorite suspect of mine.

*Ross Sullivan

*William Joseph Grant – I include him only due to recent interest. This is the suspect of Lyndon Lafferty, former CHP who spent his retirement investigating Zodiac and writing a book about it. Grant passed away even more recently at the age of 91/92, which means that at the time of the Zodiac’s killings, he would have been in his mid-40s. This does contradict some reports of Zodiac being younger, but that of course, does not rule him out. He served in the Air Force in a "troop" (can’t think of the correct word at the moment) named Zodiac and had symbols painted onto their aircraft, which is an interesting connection. This could be how Zodiac derived his name and would explain his seemingly apparent military connections. Grant also was knowledgeable in and taught cryptography. His residence also connects him to Mt. Diablo and the Peek Through The Pines card. There are other interesting connections, however where the theory begins to fall apart is when you consider that Lafferty claims there was a cover-up conspiracty due to the fact that Grant’s wife was having an affair with a powerful judge. Why the judge and law enforcement (including FBI) would be willing to cover up the most notorious serial killer in America’s history (especially considering the judge is now deceased) just to make sure they retain their health benefits is unknown to me, or to anyone with a modicum of common sense.

*Zodiac was also the Original Night Stalker – The case of the Original Night Stalker has been becoming more popular in the last 15 years or so. And, as it’s human nature to try and make connections, the theory that Zodiac also committed these murders and rapes has become more popular as well. Indeed, it is an interesting theory. I am not too knowledgeable on the case of the Original Night Stalker, or at least, not knowledgeable enough to make a claim to the validity of this theory, but it is still interesting nonetheless. Unfortunately, California in the 50s-80s had more than its fair share of serial killers, which makes it hard to say these cases were committed by the same person. But there are some similarities, especially when you consider Ted Kaczynski as the suspect (he was known to have prowled around peoples’ houses, and even broke into them and created messes, breaking things, and committing vandalism). Zodiac claimed he would alter his MO and this could have been how he had done it. Instead of killing couples in their cars or out in the open, he opted for a more safe approach, and killed them in their homes. The Original Stalker has also been known to make harassing calls to relatives of victims, much like the Zodiac is suspected to have done with Ferrin (although there are contentions to this). But the Zodiac did have a taunting attitude. He may have been able to stop sending taunting letters and change his MO, but perhaps he couldn’t let the need to rub it in go completely. A minor point against this is that the Original Night Stalker was known to be mostly active from 1979-81, and is thought to have been aged in his late 20s or early 30s, which would mean that if he were also Zodiac, he committed those crimes at a very young age – possibly under 18 in some cases!

*Team Zodiac: The Zodiac Killer was actually more than one person. How Zodiac managed to escape capture for decades is a mystery. It becomes less of a mystery when you consider that it was more than just a single man. If law enforcement were looking for one man connected to the killings who also matched the handwriting of the letters when in actuality one or more men did the killings and one or more men wrote the letters, then of course they would not make much progress. They could have even suspected the right person, but because they didn’t make this connection they let him go! Suspected letters that were later dismissed could also have been authentic in this case. Some seem highly convincing except for the handwriting isn’t quite a match. – As much as I dislike this theory, and commonly Zodiac investigators are dismissive of it, there is some evidence that could support such a thing. Most notably, the ad telling Zodiac his "partner is in deep real estate" would seem to support this. But we also can’t even know that’s related to the Zodiac Killer at all.

*The Zodiac Killer is a "hoax". I put hoax in quotes because it isn’t quite the right word to use. There were definitely people murdered, therefore someone did commit these crimes. This theory, however, states that the same person did not commit these crimes and they are not connected legitimately in any way. Someone devised the idea of the Zodiac Killer and wrote the letters, having not committed the murders themselves. This would mean also that, at the very least, they had to somehow have gotten to the Lake Berryessa crime scene before law enforcement and wrote on the car door. This also means that somehow the person that actually committed the crimes there had to have somehow known to put the circle cross symbol on their bib… yeah…

Zodiac’s Fate
*Zodiac is still alive. This is certainly not out of the realm of possibility, though the chances of this being true are growing slimmer by the day. Someone born in 1945 – about the average year assumed for Zodiac – would have been in their mid 20s during Zodiac’s peak, and today would be 70, or turning 70 this year.

*Zodiac is dead. These murders occurred roughly 45 years ago, more in some cases. It’s likely that the perpetrator has deceased since then. Being a serial killer is a dangerous life. It’s possible Zodiac made a mistake in trying to kill his next victim and was killed in self-defense. He could have succumbed to any number of illnesses. He could have simply died in an accident or old age. Really there are too many possibilities to count for what could have happened. What we do know is that this is his ultimate fate, no matter what, and that he’s getting ever-closer to it if he’s not there already.

*Zodiac is in jail. Serial killers often commit other crimes, and it’s certainly possible Zodiac could have gone to jail for something unrelated to this case and could still be there to this day. It’s one explanation for why correspondence from him suddenly ceased.

*Zodiac is institutionalized. He suffered from a mental condition that may have been getting worse, causing him to want to kill. Eventually it got to the point that he became too insane to continue his role as Zodiac and, thus, his secret vanished along with his sanity.

*Zodiac continued to kill. It’s, to my knowledge, unheard of for a serial killer to simply stop killing. BTK stopped for a long while, but then had intentions to start killing again. If Zodiac had resolved to stop killing, it’s very unlikely he kept that resolution. In fact, given the general consensus that his first confirmed murders of Faraday and Jensen were not his first, it’s even more unlikely that he simply decided to stop, and more likely that he changed his MO and/or moved out of the area.

*Zodiac stopped killing. Something in his life changed, perhaps for the better, which rid him of his need to kill. Love perhaps? However, since most consider the Zodiac incapable of being in a positive relationship with a woman, it’s more likely that he stopped killing because he stopped getting the attention he craved from the media and law enforcement. Or that it wasn’t giving him the thrill it used to and that it wasn’t worth the effort and risk anymore.

Miscellanea
*Zodiac didn’t actually live in the area. Commonly it’s thought that Zodiac lived in Vallejo, Riverside, or even San Francisco. Some, however, theorize that he didn’t live near any of those places at all; possibly not even in California. He may have only killed when he was in town or nearby on business or some other trip. It’s also possible that he moved often or just traveled a lot for pleasure and committed murders in many different places that aren’t officially connected to this case.

*Zodiac will reveal himself on his deathbed/in his will/etc. Zodiac, knowing he has outsmarted us all, will reveal himself when it’s too late for him to be put into jail. He will reveal his proof, including the remaining piece of Stine’s shirt, and possibly reveal the solution to his ciphers.

*Zodiac will never reveal himself. He has a need to prove himself superior to the world, particularly law enforcement. But that need isn’t something he shared with others, it was only for him. Simply knowing that none of us will ever know his identity is enough for him.

*Police know who Zodiac is but there’s a cover-up. Similar to William Joseph Grant, for some reason or another, the Zodiac Killer’s identity has been covered up by law enforcement. Perhaps because they are actually someone well-known or because they are someone rich and powerful that has some sway in the world of politics, law enforcement, or in general. I personally do not believe this theory at all, but it would not be the first time police did not arrest someone whom they know to have committed crimes.

*Police are reaching the end of the investigation. I’m not sure how common this theory is, as I don’t frequent Zodiac sites, but I know that there has been some talk about this. There are claims of a shadow investigation happening. We all know that the police have more evidence at hand than what we’re aware of. Sources refuse to talk much about this because of fear of endangering the investigation, including my source, so that alone should be a good indicator to the validity of this theory. What I have been able to find out, however, is that they’ve been able to narrow their primary suspects down considerably over the last few years. Most of their remaining suspects are deceased.

*Zodiac’s DNA is on file. Whether obtained through the letters or even possibly from a crime scene, law enforcement have his DNA. Suspect matching to this DNA sample has been accurate, and as such, those that the police have ruled out really are not the perpetrators of these crimes.

*Zodiac’s DNA is on file, but not from the letters or a crime scene. After being arrested for an unrelated crime, Zodiac’s DNA has been filed and entered into the database. This means that even though police have his DNA, they may not be able to connect him to the Zodiac’s crimes with it, due to so many people contaminating evidence.

*Zodiac’s DNA is not on file. The evidence has been too contaminated over time. If there was DNA from him at all on the letters, we’ll never know it. The evidence SFPD have claimed to have of him is actually not his, or it has been tainted, so that the suspects they ruled out are actually still possible suspects.