Zodiac's knowledge of Codes


Zodiackiller.com Message Board: Ciphers: Zodiac's knowledge of Codes

By Lapumo (Lapumo) (p50-30.as1.clm.clonmel.eircom.net - 159.134.50.30) on Wednesday, October 08, 2003 - 02:25 pm:

I wanted to start this thread beacuse of the many recent attempts we have seen to break the "short" ciphers in particular.While some of the comments I make will appear critical and negative,that is not what this is about.I do hope I can add something positive to these investigations while at the same time learn form those who see merit and logic in their own methodology and approach.
Personally,I see a big error in the approach.That may well be because its something I don't get and I would be greatful if someone could explain to me,what it is that I am not getting.
The big question for me,is how capable Zodiac was when it came to Cryptography.This is especially significant in relation to the small codes.Unfortunately, we do not as yet,have the answer to that question.However there are only two choices:- 1.He was an amateur 2.He was capable enough to know what he was doing.Ok,so that's obvious enough.I suggest it becomes critical though if spending time on these particular ciphers(in the manner they are being attempted)is worthwile.
If Zodiac,as an amateur, encrypted these ciphers in the manner that most are trying to decrypt them
it becomes a pointless exercise in my view.
We have now seen numerous attempts along the same lines.While some are put together better than others there isn't one of them that holds any real advantage over the other.
Let's take the bomb code as the example.
All are a variation of the same thing.We start with 32 symbols, three of which are repeated and try to find some form of words that fit the radians and inches clue.All end up in the same place. In one form or another we are so many inches on some radian.The realization then dawns that there is not enough information here and then we break our own rules in an attempt to get it to fit.In other words, we begin by taking Zodiac's clues at face value and then find ourselves introducing some new element into the equation to polish it off.
From my point of view all the information we need must be contained within the original decryption.Otherwise all we are left with is countless possibilities.
The flip side of the coin, is that Zodiac was capable enough to provide a cipher with only one possible correct answer.I have to believe this is the more likely scenario.It is not therefore, only a question of extracting enough information for the original decryption but doing so in a manner that reveals it to be correct, on decryption.That means finding a word structure that fits is not enough.We must find a structure that has a disctinct relationship with the symbols used.In other words,a math formula.
I have my doubts as to whether or not there was ever a bomb,but unless we end up with such a decryption we will end up with numerous "locations" for the bomb site and numerous names from the "My name is cipher".
There are some positive signs beginning to emerge.
I believe taking further clues from the accompanying letters and closer attention to symbols will bear fruit.Perhaps taking a look at that newly introduced "Omega" symbol might be a good place to start.
Again,this post was not designed or intended to be critical of any work done but only to ask if we need to look deeper.

By J Eric Freedner (J_Eric) (dialup-67.27.65.91.dial1.losangeles1.level3.net - 67.27.65.91) on Wednesday, October 08, 2003 - 09:13 pm:

Did any of the "usual suspects" in this case speak or write Russian? I have my reasons!

By Mike_Cole (Mike_Cole) (12-224-40-230.client.attbi.com - 12.224.40.230) on Wednesday, October 08, 2003 - 10:04 pm:

First, it's possible the Zodiac was both an "amateur" and "capable enough to know what he was doing". Creating straight substitution ciphers is not all that difficult. All it really requires is attention to symbol frequency.

Next, you seem to think that the fact the short ciphers are open to multiple "possible" interpretations indicates a lack of knowledge or capability on the part of the Zodiac. I don't believe this to be true. It's just a characteristic of short ciphers (or ciphers that have a high unique-symbol-to-length ratio). As I mentioned elsewhere, the Zodiac probably took comfort in the fact the "My name is..." cipher is open to so many possible interpretations.

I can understand your desire to have a solution that is "provably" correct. But your and my desires as would-be cipher solvers have nothing to do with the characteristics of the ciphers. Only the Zodiac's encryption techniques matter. And I see nothing to suggest that the Zodiac encoded the ciphers with any type of self-validating solution. The simplest, and therefore most logical, conclusion is that the ciphers are simple, substitution codes similar to the 408 code. If somebody shows me evidence to the contrary, I'll change my mind.

By Douglas Oswell (Dowland) (pool-151-197-185-42.phil.east.verizon.net - 151.197.185.42) on Saturday, October 11, 2003 - 07:01 pm:

Kaczynski has been said to know Russian.

By J Eric Freedner (J_Eric) (dialup-67.25.243.131.dial1.losangeles1.level3.net - 67.25.243.131) on Saturday, October 11, 2003 - 09:57 pm:

My reason for asking is that the Cyrillic alphabet is a phonetic one with certain characters standing for groups of consonents; single "characters" translate into English as SH, SCH, TH, that sort of thing. If Zodiac encrypted using such a scheme, his 13 "letters" could actually stand in for quite a few more. He may even have used one character to stand for "-ING" or other common English letter forms. This would drive cryptographers batty!

By Bookworm (Bookworm) (12-206-165-69.client.attbi.com - 12.206.165.69) on Sunday, October 12, 2003 - 06:21 pm:

Lapumo,
If Z's system was borrowed from some other code there would be a basic knowledge of code with a greater possibility of having it deciphered.

He may have to know what NOT to use in his code system to make it more indeciperable. Z would be more successful by using his OWN system, which he probably did.

By Tom Stout (Tom_Stout) (user-2ivfmbk.dialup.mindspring.com - 165.247.217.116) on Monday, October 13, 2003 - 08:12 am:

J Eric,
No one would know by my Irish name but I am a first generation American from Russian parents.
I read, write and speak Russian.
There is no single letter in the Russian version
of the Cyrillic Alphabet that represents a "th" sound.
FYI only.

By J Eric Freedner (J_Eric) (dsc03-lai-ca-204-30-131-21.rasserver.net - 204.30.131.21) on Wednesday, October 15, 2003 - 08:55 pm:

Shows you what I know, Tom! I only taught Russian for one day in college. One of my shorter job careers.

By Lapumo (Lapumo) (p50-142.as1.clm.clonmel.eircom.net - 159.134.50.142) on Thursday, October 16, 2003 - 10:36 am:

Mike you wrote;-"But your desires and mine as would be cipher solvers has nothing to do with the characteristics of the ciphers".Absolutely,we are agreed on that.
You do acknowledge though, given your analysis of these ciphers,that there many possible interpretations.We cannot as yet,say too much about the "My name is",however there is some evidence we can examine in relation to the "Bomb cipher".If we take your view,then Zodiac provided a cipher with many possible answers.Before he provides us with the "radians and inches" clue,let's put that in perspective.It is possible to find a form of words to place that bomb just about anywhere within or outside the Bay Area.
If we assume that there is a solution to the code, that only leaves three alternatives as far as Zodiac is concerned.
1.As an amateur,he did not realise at this point how vague his code was.
2.He did know what he was doing and was deliberately vague.
3.He did know what he was doing and did provide enough information to solve the code.

Perhaps we can examine these alternatives in light of his next move.One month later,he comes back with the "radians and inches" clue.
This is his third time coming back in relation to the codes.The other two times he asks how the police are "getting on with them".In other words, he has no way of knowing whether they are solved or not.This time however, he comes back with a clue.Therefore I suggest,he knows that the code has not been solved.If we are still taking everything at face value,the only way he could know this,is that was monitoring the site and was satisfied there was no activity in the area.
It also says something else though. There must have been some degree of expectation,on his part, that the code might be solved.
It's only my opinion,but it suggests to me that he did think there was sufficient information provided originally.Therefore,for me,the amateur who didn't know what he was about,seems unlikely.
So this was never an option for me,but had to be included as a possibility for diccussion.
Again,this whole discussion is only focusing on the idea that Zodiac,provided a cipher that required little other,than identifying a form of words,to match the symbols.In terms of that,what does the additional clue do for us in reality?
While it may cut down the options,it does not reduce the amount of possible answers or interpretations sufficiently enough to have real meaning.The only options I see, is that Zodiac was sending us off on a wild goose chase or he encrypted using a key.We have a couple of hundred schools and a couple of thousand miles of bus routes.If Zodiac encrypted using this method,nothing short of locating a bomb will ever prove it to be so.We haven't even begun to discuss the problems with the "Bomb" in the first place.It's highly unlikely it ever existed(at least in the form he described).
It is further evidence(to me at least)that the answer to this code will have special significance.
Let me finish by reiterating that this is not a criticism of your excellent work.All of this must continue.You have made some very interesting points and opened several positive areas for discussion, that I will come back to.Neither is it a case of me saying you are worng, you could well be correct.I just simply think there is more. I could be wrong but just want to open it up for discussion.

By Ray N (Ray_N) (66.227.204.206.bay.mi.chartermi.net - 66.227.204.206) on Thursday, October 16, 2003 - 07:18 pm:

Of course we can opine on whether he was monitoring the site or not. Or it might have been a simple matter of him knowing the code was not solved because it doesn't say anything, but he was keeping them at it and away from other potentially fruitful tasks. This is of course assuming that there is a site to begin with.

I have several problems with the whole bus bomb thingy from a purely pragmatic point of view. First of all, if we put ourselves at the point of a supposed bomb, we have to decide that we can determine when a school bus is in the projected blast area of the bomb. There are enormous problems with this. First, let's say it's a well-traveled public road that a bus is known to travel on. But there will be many other high profile vehicles on this road, a ratio much too high to produce any significant odds of blowing up a bus versus say, an Allied moving van or a produce truck or an 18 wheeler. Also, on such a road there would be a time factor involved for the light sensor to be activated, trip the firing mechanism, for the explosive charge to ignite (fertilizer is slow) and for the field of projectiles to accelerate and travel the short distance to the target. What I am saying then is that although each of these events takes only a fraction of a second, these fractions add up and there is a good likelihood that the bus would be past the bomb by the time anything could happen. I am anticipating now that someone is going to offer some way that the mechanism is going to know that the bus is coming by having the sensors remote to the explosive charge, but then we are going to have to decide how far that's going to be, and even if we have a good number for that, what are we going to do, go out there at night with a flashlight in our mouths stringing out wire and swinging a shovel hoping no one happens by? OK, you've convinced me someone is actually going to do this, how I don't know. Now we're back to blowing up a truck loaded with frozen fish or whatever. Please, I hope no one comes back with the "window counting mechanism." No, I'm afraid such a location would almost certainly have to be a location where a bus would come to a stop, where no other high profile vehicles would come. I was one of those school children Z threatened, and as I remember, there weren't too many bus stops on the highway. We got picked up in residential areas. Can you say, "Daddy, why is that man digging in our yard?" Oh, and then he's going to what? Be in the area after the bomb goes off doing some shooting? I don't think so.

We are still having the literal/figurative battle it seems, as well. What did he say vs what did he mean. Well in this particular case both sides can have it either way. What strikes me as important is that he told us later he was fooling with our heads and had no intention of doing any bombing. Frankly, that's almost like him saying he had no plans to blow up Cheyenne Mountain after all. Not quite so monumental a task, admittedly, but ridiculous all the same, however seriously taken by the authorities, who had no choice in the matter. And if we go there, one guess at the solution to the code is as good as the other thousands of possibles. Let's just face the overwhelming probability that he was just laughing his head off while the cops followed the school buses around, like Jack was amused by the antics of Scotland Yard and the London media. Simply put, he was conducting a test of his power, IMO. When you think of it, he never made a threat that he followed through with. It was all just posturing and posing to get his way with the papers and public opinion to the frustration of law enforcement. A nice little power trip.

So I rather think that there is much less than meets the eye here, rather than more - a position I will maintain until somebody blows themselves to bits poking around Stevens Canyon Rd. at which time I will promptly apologize to the deceased. In the meantime, good luck with the Easter egg hunt. :)

As always, these are my thoughts, not necessarily yours.

By Mike_Cole (Mike_Cole) (12-224-40-230.client.attbi.com - 12.224.40.230) on Friday, October 17, 2003 - 12:19 am:

Lapumo,

I agree that there are many possible solutions to the cipher. I further agree there are many possible locations that are reasonably consistent with that described by the Zodiac (i.e. north-south road with a hillside on the west). However, I do not agree with the assessment that "It is possible to find a form of words to place that bomb just about anywhere within or outside the Bay Area." Many of the possible solutions will not be very meaningful, let alone meaningful within the context of identifying a bus-bomb location. When such a solution is found, it should be evaluated on the basis of its merit.

Both you and Ray (and probably several others) appear to be of the following opinion: since there are many possible solutions and no one solution is provably correct, there is no point attempting to solve the cipher. While I understand and respect this opinion, I don't agree with it. The tasks of attempting to solve the ciphers and evaluating the relative merits of proposed solutions likely holds the key to a better understanding of the information involved, even in the absence of a provably correct solution.

For example, I don't know if my proposed solution is correct. However, I've made some interesting observations about the Johns letter since finding the solution. Namely, (1) "inches along" straddles the "6" line of the zodiac symbol. (2) The circle of the zodiac symbol starts and ends in the 6 position. (3) The postscript is centered on the 6 position of the zodiac symbol. These observations, a by-product of my proposed solution, lead me to believe that the Zodiac is trying to communicate something about the 6 position (even if my proposed solution is not correct).

One final thought somewhat related to your post. The task of creating a cipher is usually done with the intention of preventing undesignated people from deciphering it. Doing this is probably relatively easy if one acquires some basic knowledge. However, the intention of the Zodiac was likely slightly different. In particular, he likely wanted his ciphers (with the possible exception of "My name is...") solved after some amount of time. Although I have no specialized knowledge on the subject, it seems to me that creating a cipher that can be solved after a non-trivial but predictable amount of time is a task that is substantially more difficult. The Zodiac appears to have done a reasonably good job with the 408 code, although it may have been cracked sooner than he would have liked. He appears to have not done such a good job with the other two (assuming they are solvable and he wanted them solved).

By Mike_Cole (Mike_Cole) (12-224-40-230.client.attbi.com - 12.224.40.230) on Friday, October 17, 2003 - 12:26 am:

Ray,

Assuming the bus-bomb diagram is reasonably accurate, the bomb is only "armed" between approximately 9:00-10:00 am. This helps with but does not eliminate the issue regarding other trucks, etc.

By Tom Voigt (Tom_Voigt) (12-231-193-32.client.attbi.com - 12.231.193.32) on Friday, October 17, 2003 - 12:36 am:

I believe opposing mindsets (if that's the case) such as Sean/Ray/Mike's are essential.

Good job, guys!

By Lapumo (Lapumo) (p50-243.as1.clm.clonmel.eircom.net - 159.134.50.243) on Friday, October 17, 2003 - 04:20 pm:

Absolutely Tom,I don't even think I would call it "opposing mindsets" more like looking at solving this problem from different angles.
On that score Mike,my position is certainly not a case such as you have outlined above.(That we shouldn't bother because there are so many solutions)I have spent the last few years doing little else. We must make every attempt to solve these.
I am 100% in agreement that each "solution" must be evaluated on the basis of it's merit.
One other comment you have taken out of context.When I said "It is possible to find a form of words to place the bomb just about anywhere within or outside the bay area" I was speaking of the conditions that existed when Zodiac gave us the initial information.This was before the Radian and inches clue arrived.
Let me refine that further.I can't give exact figures,but for the purposes of making the point I want to make,let me give the following example.
I think the number of bus route miles was somewhere in the region of 4000 miles.I can't begin to guess at how many possible sites there would be that would fit Zodiac's criteria.However if there was 1000,let's say,I'm claiming that a form of words could be fitted into his code that would cover the majority of those.
All one has to do is align his "compass" to magnetic north. There's nothing stopping me from picking any direction thru 360 degrees or any measurement that suits or any other variable I want to introduce.
I'm not satisfied that the extra clue of Radians and inches, cuts down the amount of possibilities enough to have real meaning.We can't get away from the fact,that nothing short of locating a bomb would be sufficent proof that your method was correct.
Having said that, your observations regarding the number 6 are compelling.That's of course if we are not looking at something else here, other than taking this puzzle at face value.It's well worth investigating this clue further.
Perhaps it would help to tell you what I believe and then you might better understand where I am coming from.While I believe there is a "location",I don't believe there was ever a bomb, such as Zodiac described anyway.
His supposed bomb wasn't actually one bomb but a string of five,spread over a distance of at least 60ft.Each containing One bag of ammonium nitrate, a gallon of stove oil and a "couple" of bags or gravel.While there are major questions regarding transporting, burying and wiring all this material up,his big problem is the Ammonium Nitrate.There is little to no chance of this remaining intact,buried over a period of nearly three months.He makes no mention of pipes, but it is entirely possible he needs these to direct the blast. This substance can't be stored in such confinement.If it's exposed to the earth it will be absorbed.It is also highly soluable,so any rain will just wash it away.Any exposure to zinc ,copper etc will cause it to degrade as will exposure to extremes in temperature.(Which one is bound to get). He certainly cannot mix it with stove oil at the time he buries it.
So even in the unlikely event he does manage to overcome all these problems,he has to come back to finish the job.Is this something he is willing to risk ,if he has given the location away?
Even if he is, there's a very real chance this would literally,blow up in his face.
This is the type of bomb that would work by putting it together in a very short period.However it's highly unlikely to be a successful operation, as he describes.
So really ,it's a combination of different things that lead me to believe there was something else at play here.
One possibility,is that he had reasons for wanting to see if police showed up at a particular location.
Please do keep it going Mike.I sincerely hope my opinions and comments have not had a negative effect.I believe there is real progress to be made in this area.

By J Eric Freedner (J_Eric) (dsc03-lai-ca-206-217-9-28.rasserver.net - 206.217.9.28) on Saturday, October 18, 2003 - 11:58 pm:

The only vehicle Zodiac was ever known to operate was a car. If he was going to set up this bomb, are we to conclude he would have put 5 sacks Ammonium Nitrate, 5 gallons of stove oil, and a couple of bags of gravel in his back seat?

And why call it "stove oil"? No one in California calls kerosene that. Figure out what part(s) of the country "stove oil" is used in as of the 60's, and that's probably where the originator of the bomb formula hailed from. I think it's in parts of the Deep South, Georgia, South Carolina?

I've always figured Zodiac got the formula from some book (they do have stuff out there like how to get even with anyone, how to make nasty bombs, etc.).

IF there was a real bomb, I still think it would be used to blast a water source (hydrant, dam) or make cars fall into water (bridges).

By Mike_Cole (Mike_Cole) (12-224-40-230.client.attbi.com - 12.224.40.230) on Sunday, October 19, 2003 - 11:56 am:

Lapumo,

I agree with much of what you say. The only real disagreement we have concerns how difficult it is to come up with a meaningful and otherwise viable solution for the Mt. Diablo code. In the end, this is pretty minor.

The practical problems that you point out may well have contributed to the Zodiac's ultimate inability to do what he described. My personal opinion is that he probably wanted to build and install the bus bomb, but eventually concluded the project was beyond his capabilities (at least in terms of doing it effectively).

By Warren (Warren) (64.221.18.62.ptr.us.xo.net - 64.221.18.62) on Monday, October 20, 2003 - 07:03 am:

I too was struck by the term "stove oil". I can only speak for Texas and have heard many older people refer to it.

By Lapumo (Lapumo) (p50-100.as1.clm.clonmel.eircom.net - 159.134.50.100) on Monday, October 20, 2003 - 09:27 am:

Perhaps it was a simple case of him having an oil burning stove as an alternative to an electrical appliance.Cabin/Trailer!

Mike
Did have a few questions for you in terms of how you see the bomb solution as it relates to other "Radian theories".
There were two things in particular that I liked about your "bomb solution".I not only liked your reasons for coming up with the direction along "six" but also that it complimented the information Zodic gave us.Simple and straightforward.In other words,Zodiac gave us the drawing with positions 0,3,6,9 and the possible answer,(given the limited code length)may simply relate to one of these directions.
If that proved to be the case, does it not imply that when Zodiac used the word "Radians" he was simply relating to the linear directions (of 0'3'6'9) as opposed to any angular measure?
In other words,he may well have meant "Radaii".
I know you have suggested elsewhere that he did not use "Radian" in its full technical sense but rather as an angle of 60 degrees.Yes,I know,the two are somewhat related here in that position six does relfect an angle of 180 degrees.But that would be the "third Radian would it not? (At least in terms of your argument).
Do you see two seperate theories,one an extension of the other,or do you feel your solution(if correct) accounts for this "radian" once and for all.
Anyone else have a comment on this?

By Eduard (Eduard) (ip503dbace.speed.planet.nl - 80.61.186.206) on Monday, October 20, 2003 - 02:22 pm:

Lapumo,

The 9 from the positions of the drawing (with 3 and 6 etc) looks more like a q to me...

Eduard

By Eduard (Eduard) (ip503dbace.speed.planet.nl - 80.61.186.206) on Monday, October 20, 2003 - 02:53 pm:

Here is a close-up....

q or 9

Eduard

By Eduard (Eduard) (ip503dbace.speed.planet.nl - 80.61.186.206) on Monday, October 20, 2003 - 03:22 pm:

Yes, I definately think that character is a "q" (see below for explaination)...

q or 9?

Eduard

By Mike_Cole (Mike_Cole) (12-224-40-230.client.attbi.com - 12.224.40.230) on Monday, October 20, 2003 - 08:35 pm:

Eduard,

Many people write nines like this. Given the context (0, 3, 6, ?), I see no reason to conclude the character is anything other than a '9'.

By J Eric Freedner (J_Eric) (dsc01-lai-ca-199-35-205-143.rasserver.net - 199.35.205.143) on Monday, October 20, 2003 - 09:35 pm:

IF you are going to say it's a lower-case letter (rather than the number 9), it could just as easily be a "b," "d" or a "p" as in my concept of Zodiac's encryption, he sometimes flipped letters around to throw decoders off track.

But as far as I am concerned, "me a nine." It's even in blue, making a "blue meannie."

By Mike_Cole (Mike_Cole) (12-224-40-230.client.attbi.com - 12.224.40.230) on Monday, October 20, 2003 - 10:00 pm:

Lapumo,

Let me clarify my beliefs regarding "radians"... Radians, like degrees, are particular units of angular measure. I believe the Zodiac's clue (radians and ...) refers to the generalized notion of angular measure, irrespective of any unit. My interpretation of the clue can be paraphrased as: "...concerns an angle and # inches along the angle". As Ray once pointed out to me in a conversation, "inches along" an angle (measured in radians or whatever) doesn't make strict, conceptual sense. However, I believe this is an informal reference to a polar-coordinate type specification. With polar coordinates, points are identified by a radius and an angle. The angle is measured from an implied polar axis - in our case this is probably the 0 ray of the annotated zodiac symbol (0, 3, 6, 9).

BTW, the use of the arguably esoteric unit, radians, may have been intentional - an attempt at obfuscation by focusing attention on the unit. If it was intentional, it was very intelligent given how well it's worked.

I don't mean a "radian" should be taken as 60 degrees. What I've said is the following. When one looks at the evidence, there are multiple references to a circle divided into 12 equal segments (30 degree slices). Further, the angle that people have claimed is an approximation of 1 radian (BRS - Mt. Diablo - Stine) is quite likely an approximation of 60 degrees (two consecutive 30-degree slices).

So, in the end, I don't think the term "radians" is a reference to radii directly. Personally, I would be comfortable with any solution that used any of the implied rays, 0-11, not just 0, 3, 6, 9. However, due to the other clues/evidence we've discussed, I do believe the 6 ray is the correct one, even if my solution is not correct.

By Howard Davis (Howard) (pool0820.cvx30-bradley.dialup.earthlink.net - 209.179.143.55) on Monday, October 20, 2003 - 11:49 pm:

Eduard,
It's good you are pointing out what you believe about a Z map 'number' which you see as a q.
On BHs door we find Zodiac used a 9 twice and in both cases '69 (or the number 9)is clearly a number and appears to resemble the '66 map 9-which is a multiple of three as per the map degrees-3-6-9.A q would not seem to fit the numerical sequence
I have carefully studied Z's writing since '87 and it seems like his 9.
Two views, but I should mind my p's and q's!

By Eduard (Eduard) (iproxy4.kennisnet.nl - 212.178.7.55) on Tuesday, October 21, 2003 - 04:25 am:

Mike, J Eric and Howie,

For building up a theory it is important if it is a q or a 9.
But you are all right in your reply....

Eduard

P.S. Is that a zero or the letter "O" we see in the crosshair? :)

By Lapumo (Lapumo) (p51-125.as1.clm.clonmel.eircom.net - 159.134.51.125) on Tuesday, October 21, 2003 - 07:45 am:

Have to agree with all the other comments Eduard.
Was this just an observation or have you something
else to back it up?

Thanks Mike.

By Eduard (Eduard) (squid-test.kennisnet.nl - 212.178.7.60) on Wednesday, October 22, 2003 - 03:45 am:

Lapumo,

At this point in time I think it's just an observation but maybe it can lead to a new theory...

Eduard

By Howard Davis (Howard) (64.30.222.97.lcinet.net - 64.30.222.109) on Wednesday, October 22, 2003 - 09:58 pm:

Eduard,
Z seems to have made a very darkened "O"or zero, to represent the continuing failure of the police to apprehend him-he's bagged "13" and the count for their quarry ,Zodiac, is a large dark zero,thus the extra ink job for emphasizing this fact.
The cue is the pattern from past counts and circle/crosses along with,in this instance,a big 13 compared with a large O.
As a criminal and an elusive one at that,Z must have greatly delighted in knowing that in spite of all the authorities efforts to capture him, he remained free.
He was accomplishing his goal,but they were not fulfilling their desires of incarcerating Zodiac.To a wanted hard core criminal,this is a grand state to exult in for sure-he drove home this feeling whenever he could,this "O" being another example!