Bus Bombs

Zodiackiller.com Message Board: Letters: Bus Bombs

By Mike_Cole (Mike_Cole) (12-224-40-230.client.attbi.com - on Saturday, October 25, 2003 - 12:27 am:

I'd like to start a discussion regarding the two described bus bombs.


The first bomb was described in the bus-bomb letter.




The second bomb was described in the My name is... letter.


B A Situation
Dark Dark Bomb disabled - night or "cloudy" day
Dark Light Bomb disabled - unlikely - possibly cloudy scenario
Light Dark Bomb explodes
Light Light Ready and waiting for bus



IMO, these two bombs represent a "technical evolution". That is, the second is clearly superior to the first. Because of this evolution, it's my opinion the Zodiac likely experimented with at least the triggering mechanism of the described bombs.

By Nick (Nick) ( on Saturday, October 25, 2003 - 02:52 am:

While Z doesn't specify an ignition source in the diagrams, it's pretty safe to assume this type of bomb would require a blasting cap for detonation. Unfortunately, in that era, commercial and military grade caps (typically mercury fulminate based, 6-8 grains) were readily available and purchases were rarely traced. Otherwise, Z might have left a paper trail (of course assuming he wasn't BS'ing and actually constructed such a device). Today, terrorists and would-be anarchists make their own detonators to avoid tracing. Z might have done the same back then if he was as paranoid as seems. In that case anything ranging from a large firecracker to a fused C02 cartridge would suffice. That, however, requires some off-site packaging to get the proper compression ratio and at the same time avoid blowing oneself up.

By Tom Voigt (Tom_Voigt) (12-231-193-32.client.attbi.com - on Saturday, October 25, 2003 - 12:32 pm:

Mike, I think you're right. Good job.

Showing a progression would have surely given authorities the idea he was truly experimenting, hence adding validity to his threats. The question is, did this experimenting happen around the time of the letters, or had he already been through the process?

By J Eric Freedner (J_Eric) (dsc03-lai-ca-204-30-131-17.rasserver.net - on Saturday, October 25, 2003 - 08:52 pm:

I for one don't think Electric Eye mechanisms were as readily available back in the 60's as they became later on.

Remember Zodiac's "Electric Gunsight"? Mere flashlight atop a firearm!

So the Bomb Electric Eye could also be pseudo-scientific babble. My best guess as to the actual bomb design: a magnifying glass set up to catch the morning sun's rays at a certain hour, focusing them onto something to start a detonating fire.

By Mike_Cole (Mike_Cole) (12-224-40-230.client.attbi.com - on Saturday, October 25, 2003 - 11:03 pm:

A particular segment of my misspent youth included a fascination with all things explosive. This passion was shared by my then best friend, Tim. Together, we engaged in numerous pyromaniac exploits. In the end, they were all harmless, although most were potentially dangerous.

Much of our inspiration was drawn from two sources. The first was a little black book that, as I recall, didn't even have a title. The second, decidedly more interesting, book was purported to be an Army training manual. I remember the title well, but I prefer not to post it here... Let's just refer to it as "Manual X". Both of these books were purchased at gun shows.

As you likely have guessed, Manual X (and the black book as well) contained considerable information about the construction of bombs and bomb-related components. Although my recollections are somewhat vague, I'm quite certain the clock-based detonator described by the Zodiac was in the manual. I'm sure I don't remember it better because I considered it to be somewhat boring. There were more interesting detonation devices, such as a pressure-based altimeter-sensing device.

Furthermore, Manual X was the first place I ever heard mention of using "ammonium nitrate fertilizer" in the construction of a bomb. Additionally, I specifically remember a described bomb that involved a fertilizer-based explosive in conjunction with 1 gallon of gasoline. The manual may have even listed alternative, flammable liquids; one of which may have been something equivalent to "stove oil". Gasoline sticks in my mind because that's what was readily available to us at the time.

Manual X appeared to be relatively old at the time we were using it. In fact, it appeared to me to have a Vietnam-era look and feel to it. Therefore, it's a possibility that the Zodiac was partially inspired by Manual X or some similar type book.

By Ray N (Ray_N) ( - on Sunday, October 26, 2003 - 08:38 am:

Please allow me to interject even more technical problems which, in my opinion, would make both of the above described types of bombs unworkable.

In the first, we have a flashlight beam with a light source of a single bulb with a voltage of either 1.5 or 3 volts being driven by a 6 volt battery. It doesn't take an engineer to tell you what effect this would have on the filament of said bulb. (Plus there's no solar panel to keep the battery charged. No matter, the bulb won't last long enough to make a difference.) Add to this that the beam is "focused" by a cheap, shiny plastic reflector, travels down a length of blackened tube, absorbing a fair amount of the puny output, and then it has to travel all the way across the road and then back to the photocell.

Let me illustrate the problems with this by describing a similar device used in aviation. The device I am referring to is called a transmissometer. When pilots are preparing to conduct an instrument approach in low visibility, one of the crucial pieces of information the pilot gets from the tower is the runway visual range (RVR). This is reported ground visibility in hundreds of feet as measured in the touchdown zone by the RVR equipment (the transmissometer). The device consists of a high intesity, highly focused beam of light aimed down the side of the runway to a receiver at a known, fixed distance. A computer compares the known light output vs the intesity of light received, and computes a visibility value based on a factored difference of these two values. The more fog there is, for instance, the less light makes it to the receiver, and the lower the visibility. Each RVR would then have a certain threshold value in terms of the ratio of the above values, one a constant, and the other measured. In order to factor the ratio, many other parameters are evaluated by the computer, such as time of day, sun angle and azimuth (ie, julian date), whether it is raining or snowing (reflection off of particle precipitates), etc, etc. Other light sources are also considered such as runway and other airport lighting at night. In short, it is a fairly complicated calculation. Granted, the results that are desired require more discrimination than would a simple on/off value, however a threshold value would still have to be determined. In other words, light or dark isn't good enough. We'd have to know how light vs how dark. Otherwise the bomb would either not work or would blow up at an indescriminate time. The fact that we would have sunlight coming in from the east competing with a puny reflection of a flashlight bulb would require extremely sensitive equipment to detect. There's nothing here even approaching that. He may as well have used a candle with a wind guard. It's ridiculous.

I suppose the second bomb may be described as a technological evolution, in as much as flint is an improvement over rubbing two wet sticks together for starting a fire. This one is better and worse at the same time. It's better in that it at least attempts to utilize a reliable light source. But the location of that light source is now moving. Since it (the "sunbeam") must be captured within a small apeture, an account must be taken of where the sun rises on the horizon, which changes fairly appreciably every day. At best we might be looking at a 3 day window of opportunity. But wait, it gets worse. Since we have the "arming timer thingy" involved, we can't just track the sun along the horizon, we have to continuously track it's elevation as well, throughout the entire "armed" period, with some method to align the receiving tube both horizontally and vertically to capture the sun at a precise, moving point in the sky. And, unfortunately, that point in the sky would necessarily have to be computed to constantly remain on a line of sight that would be broken by a bus, but not a car. This is a very tall order for something made out of paper tubes and shoe polish.

In short, neither one would stand any chance of doing much except blowing up unexpectedly. It's very juvenile in concept, and it's not anything I'd get within range of. This reminds me of a cartoon contraption where the wind blows on a vane which pulls out a plug in a jar and lets the water run out, unbalancing a lever which drops a rock, which tightens a cord, which pulls a leaf off of a magnifying glass which focuses a sunbeam on the end of a fuse. I can so visualize Zodiac being very amused with his ability to cause so much calamity with a simple drawing.

I'll take the opportunity to point out how strongly this points away from Kaczynski. The drawings were messy, and the logic and planning are unsound.

I guess all this just goes to show the continuing power of Zodiac. A simple threat, a self-admitted hoax, is still driving so much inquiry and investigation some thirty years after the fact. Truly amazing.

By Douglas Oswell (Dowland) (pool-151-197-209-239.phil.east.verizon.net - on Sunday, October 26, 2003 - 09:42 pm:

Ray, you don't need to be very meticulous when all you're out to do is cause a public reaction. You might want to see my comparison of one of Kaczynski's "real" bomb sketches with Zodiac's 1970 drawing at http://mysite.verizon.net/douglas.oswell/p8.html. During the Zodiac years Kaczynski hadn't perfected his bomb-making technique. It took at least a decade of on-and-off experimentation before he produced a device that was powerful enough to maim or kill.

Kaczynski was smart enough to know that once you've achieved a certain level of credibility you can scare the public and make the authorities jump through hoops without any kind of sophistication whatsoever. With Kaczynski it was the 1995 threat to blow up an airliner. With Zodiac it was a hastily drawn sketch, which, as you've pointed out, is still hoodwinking people who should know better.

By Mike_Cole (Mike_Cole) (jffwpr04.jf.intel.com - on Monday, October 27, 2003 - 12:52 am:


Why do you characterize the bus-bomb threat as "a self-admitted hoax"?

By Ray N (Ray_N) ( - on Monday, October 27, 2003 - 04:03 pm:


You have a good point there. Maybe we can't exclude Ted on the basis I suggested.


Because no bomb was ever detonated or found, and because Zodiac wrote that people who thought he actually intended to carry out an attack such as he described had holes in their heads?

Anyone wanting hours of fun might try going to Radio Shack and setting up such an arrangement. Don't bother with explosives, of course, just get the circuit to light up an LED or something when the sensor is tripped.

By Ray N (Ray_N) ( - on Monday, October 27, 2003 - 04:27 pm:

Actually, a similar type of device has been used successfully, but there was a person at the scene to arm the bomb by remote control just as the target vehicle approached, avoiding problems like tracking the sun with a toilet paper tube. As I recall, the projectile in this case was a single 4 pound piece of plate steel.


By Douglas Oswell (Dowland) (pool-151-197-224-234.phil.east.verizon.net - on Monday, October 27, 2003 - 05:27 pm:

When you compare the actual killings with the bomb threats, the latter seem almost in the way of jokes. There isn't even anything sinister in them, so far as content or tone are concerned. It probably tickled Zodiac no end to think that there were people out there taking the bomb threats seriously.

By Mike_Cole (Mike_Cole) (12-224-40-230.client.attbi.com - on Monday, October 27, 2003 - 06:15 pm:


IMO, it's incorrect to apply the "holes in your heads" comment to the bus-bomb threat. Please allow me to explain by listing the relevant bus-bomb events in chronological order:

One could argue that since the original school-bus threat was a "self-admitted hoax", the bus-bomb threat is more likely to be a hoax. But I don't think it's fair to characterize the bus-bomb threat itself as a self-admitted hoax.

By Douglas Oswell (Dowland) (pool-151-197-224-234.phil.east.verizon.net - on Monday, October 27, 2003 - 06:30 pm:

Mike, I think Zodiac's "radians" hint was given for the same reason as his ciphers; namely, so he could amuse himself by watching the authorities jump through hoops, and perhaps, further, to maintain the thrill of seeing himself making regional or even national news. All his threats of mass murder, beginning with the August, 1969 letters, turned out to be nothing more than bombast.

By Howard Davis (Howard) (pool0723.cvx16-bradley.dialup.earthlink.net - on Monday, October 27, 2003 - 11:56 pm:

Good posts Mike!

By Ray N (Ray_N) ( - on Tuesday, October 28, 2003 - 09:02 am:


In light of your argument, I agree that the bus bomb was not necessarily a hoax. And you are right, he did not specifically refer to the bomb but rather the shooting out of the tires when he used the "holes in the head" phrase.

Still, we must face the facts that any attack on a bus with a bomb such as he described would have been frought with technical problems. Such a bomb would have been dangerous to deploy and the subject would have been at high risk of being witnessed while setting it up. The bomb components would have been exposed to the degrading effects of the elements over a relatively long period of time. And, in order to work, even if all of the above were not factors, the device would have had to have been far more advanced in design to have even worked at all. We could in all fairness call the designs submitted by Zodiac Chapters 1 and 2 of "Roadrunner Bombs by Wil E. Coyote."

So, notwithstanding that I was wrong about what Zodiac actually admitted was a hoax, there remains the inescapable extreme probability that the bomb threat was one nonetheless.

By Ray N (Ray_N) ( - on Tuesday, October 28, 2003 - 09:04 am:

Yes, Doug. In fact, Zodiac never followed through on any threats that he made. He didn't have to. He had already established his "credibility."

By Douglas Oswell (Dowland) (pool-151-197-40-164.phil.east.verizon.net - on Tuesday, October 28, 2003 - 04:28 pm:

It's almost as if by the middle of 1970 he had completely lost interest in whatever game he was playing. In my opinion, by the time he reached that point he had gotten whatever was bugging him out of his system; or at least enough so that it wasn't worth his life continuing. He amused himself a bit more with the strange letters and odd threats, but for the most part the Zodiac episode was at an end.

By Mike_Cole (Mike_Cole) (12-224-40-230.client.attbi.com - on Tuesday, October 28, 2003 - 10:15 pm:


You are probably right about the Zodiac's intention with respect to the radians clue. However, assuming you are correct, it's still possible the clue does, in fact, have some specific meaning.


I agree there are numerous practical problems with someone effectively using either of the described bombs to blow up a school bus. And you may well be right that the whole thing was a hoax from the very beginning. Yet, I still consider it a possibility that the Zodiac intended to do as he described initially and later concluded such a project was impractical.

By Nick (Nick) ( on Wednesday, October 29, 2003 - 01:14 am:

Whether or nor he actually attempted to carry out the plan, it does seem he became obsessed with the idea of a school bus assault. If his only motive was to gain amusement or widespread fame via mass hysteria, he likely would have threatened to blow up something like a commercial jetliner.

By Douglas Oswell (Dowland) (pool-151-197-45-236.phil.east.verizon.net - on Wednesday, October 29, 2003 - 02:31 pm:

Which incidentally, Nick, is something Kaczynski finally got around to in 1995.