There are many different views on these topics here. My personal belief is that Zodiac was responsible for Lake Herman Road, Blue Rock Springs, and Presidio Heights, and these are the ones he specifically took credit for in his letters. The MO is basically the same – Find victim(s), shoot, escape.

Lake Berryessa is a whole different thing. It involves that elaborate costume, was a knife attack, it’s during daylight, and so on. The descriptions of the LB and PH attacker are considerably different, and both crime scenes had multiple eye witnesses. The letters do not claim credit for LB (only crimes in the "north bay area"), and the car door at LB does not list all the months of activity that the letter writer does (namely, AUG.)

Anyway, you can read through the related topics here and see many different opinions. I started out believing it was all the work of one guy, but gradually decided the notion they were different people made more sense. In fact I wouldn’t exactly call the Berryessa killer a "copycat" because he really didn’t copy much of Zodiac’s MO at all – just the taunting on the car door. Other than that the crimes are quite different in almost all aspects.

Thank you for your answer. Zodiac did hint in writing that he may have stabbed hartnell and Sheppard as he said by rope by gun by knife. I am of the opinion that the guy was likely the one and the same

That’s unless Marshall, that you look at the Pre Zodiac suspected murders. It does match his MO if he was responsible the Domingos/Edwards murders as well, and the Swindle murders certainly match his MO.

"Lake Berryessa is a whole different thing. It involves that elaborate costume, was a knife attack, it’s during daylight, and so on. The descriptions of the LB and PH attacker are considerably different, and both crime scenes had multiple eye witnesses. The letters do not claim credit for LB (only crimes in the "north bay area"), and the car door at LB does not list all the months of activity that the letter writer does (namely, AUG.)"

Presidio Heights is a whole different thing, it involves removing part of a shirt, was a gun attack in the heart of the city, with streetlights, and so on. The descriptions of the LB and PH attacker are the difference between a haircut and dye, and both crime scenes had multiple eye witnesses. The letters do not claim credit for LB (apart from Sept in the Dripping Pen Card, which hasn’t been attributed to any other crime of relevance), and the car door at LB does not list all the months of activity that the letter writer does (namely, AUG.) But lists all the crimes he knew we were aware of.

The point of this analogy, is that if the Zodiac hadn’t mailed the piece of Stine shirt, we would have laughed at the suggestion this was a Zodiac crime during October, based on its complete departure from the first two crimes. Even after the Bus Bomb letter, many would have said Zodiac was claiming a crime he didn’t commit. The shirt allied to the October 13th letter is the only thing that probably would have convinced us.

Of course it doesn’t shock most here who know me when I say I agree with Marshall. A costume, a knife, and daylight…a whole different scenario…and physical size and, apparently voice too. My thoughts have certainly been expressed enough elsewhere at this site. There are plenty of threads here guild1995, with some great thoughts and varied opinions.

Wasn’t it confirmed the handwriting on Hartnell’s car was a match with Z’s letters ?

It looks like a match to me.

I personally think that there was originally one killer and a partner/friend writing the letters, and then a second killer (who became part of the "team" at some point) committed the Stine murder. If I had to guess, I would say that all three men on "team Zodiac" were at Lake Berryessa, hence the letter writer being there to write on Hartnell’s door. One thing I wondered is if these three men were at the lake to "initiate the new guy." The new guy being Stine’s killer, of course.

Some serial killers change their methods of killing to confuse authorities, whilst others may keep to the same M/O for their signature, as we voyeurs into this macabre world recognise. Zodiac did stick to his M/O all along if the ‘by gun/knife/rope/fire’ card is something to go by, and he was willing to risk all by communicating his intentions and what he has done. So, anyone murdered by any of these methods could in theory be attributed to the Zodiac, or he could claim them with knowledge reported in newspapers or through other communications by ‘comrade-killers’ as they may be called. (Strange how Zodiac missed the most common element that is water out in his methodology, but that can be discussed in another thread.)
However, these are probably 4 of the most probable and easiest ways to kill people (not forgetting the water), so this may give a means for Zodiac to ‘claim’ kills not made by him as some theorise. This may also give a team the means to kill if they are focused on the same goal- to spread terror and diversion, whilst they go about doing their own thing with less publicised kills, or until they meet up to do joint kills.
That’s one of the theories which weigh heavily in my mind, alongside the possibility that maybe there was a lot of mentoring going on. If Zodiac had links to say Atascadero or Deer Lodge, or was even a member of the Church of Satan (with less publicised kidnappings out of the Zodiac limelight ending up as black mass sacrifices as some speculate), then one thing is for certain- there is the stink of a conspiracy going on, if the lone wolf theory is to be challenged, when it comes to Zodiac.
Another possibility could be that the 12 kills of Zodiac (the kill and escape murders) were a trial, like some kind of hunter’s challenge, and when it turned out to be successful, Zodiac had his reward (12 slaves in paradice) and changed his tact to kidnap/play with prey and reap the reward/kill/dispose.
Wouldn’t it be ironic if the main suspects were part of this? Kane/Allen/Ed Edwards (fit who you wish into here) being prime three, with a private hunting lodge up north or near Lake Tahoe, where they went on kidnapping and killing for years to come?
Was there a killer’s club in SF and California through the 1960s?
Well, the CIA was dosing the population with LSD and other drugs during MK-ULTRA and Midnight Climax operations as evidences reveal, so why not MK-ZODIAC or such a kill-club? To me, it sometimes makes more sense than the solo gunman, but even this speculation lacks conjecture without evidences.
Anyone got any further theories on the killers club aspect?
Just for a bit of fun- looking at the 340 cipher- does Kirt, Renolds, Smit (or Smith) and Dyk stir any suspect thoughts? Would like some info on these possibilities (if they exist) so I can recheck something I’m working on. If it makes sense then I will post this technique end of week, but still scouting for info. at the moment.