I'm glad my Bungie letter interests you. I'll give you the full story, to clarify the nature of the letter and the circumstances under which it was written...
I suppose the Marathon experience has been the same for many of us - on the one hand we enjoy trying to piece together the fragmented storyline from the enigmatic clues and hidden messages, but on the other our piqued curiosity demands satisfaction. I completed the game, absorbed the evidence, and wanted some form of resolution. I was utterly oblivious to the various opportunities for Marathon discussions available on the internet, so I decided to pose my questions to Bungie directly. I would not dare attempt such an activity today, as it would prove fruitless thanks to the veil of secrecy Bungie have rightly chosen to draw over the expanded marathon plot. But I suppose in those days secrets weren't so closely guarded, and the reply I received from Doug Zartman was slightly more lucid than the cryptic messages Bungie now seem to like torturing you with.
Most of my questions centred around the discrepancy between the screenshots I had seen in magazines and the final product, (I was very young and naive, and unaware that "a game in development is a very fluid thing"). Nevertheless, there are three points which I believe may be of interest to Story Page readers. The first concerns the number of levels in the game. Mr Zartman stated that:
"There are in fact only 37 levels. Sorry, we tried our damnedest to make 40 awesome levels, but when it came down to the wire, only 37 qualified as good enough for inclusion. As Christmas approached, the pressure to wrap it up and get it out became overwhelming, and the 37 levels which were finished provided a nice long game."
I seem to remember reading somewhere on the Page that several Pfhor levels, while being wonderfully atmospheric in their ambiguity, seem to lack any clear objective. The suggestion was raised that other levels had been planned, but never completed. Maybe these "connecting" levels are precisely what Mr. Zartman is alluding to here, and they may exist in a partially-completed form somewhere in the Bungie offices. Just a thought.
The letter also states that:
"You are right - the tenth cyborg that Tycho knew about but Leela didn't is 'you' - the main character. We didn't want to make that explicit in the game, but clever players are supposed to figure it out."
You knew this already, of course. The clues became increasingly noticeable as the games progressed. But it is reassuring to have one's theories confirmed by Bungie themselves. Note also that "Tycho knew about" the tenth cyborg, but Leela did not. Apparently Leela was totally unaware that the individual she guided around the Marathon was a cyborg, although as other contributors have suggested, some of her slightly garbled terminal text does indeed make reference to such phrases as "Mjolnir Recon number 54." An interesting disparity. And how is it that, by Mr. Zartman's own admission, Tycho was aware of the cyborg presence, while Leela was not? Why was the information known to two of the AIs but not the third? Of course, it is always possible to interpret Mr. Zartman's comment as meaning that Leela never made reference to the tenth cyborg, whereas Tycho did...
The final point concerns Bernhard Strauss. I was concerned that he seemed to suddenly and inexplicably vanish from the storyline, as if forgotten. The letter reads:
"Ahh, Bernhard Strauss. No, Durandal did not forget about him. In fact, Strauss was the only being Durandal was afraid of. While you were on the alien ship, Durandal learned Strauss was no longer a threat to him. I have a feeling we haven't heard the end of this story."
To be perfectly honest, I sincerely doubt we've heard the end of ANY story in the Marathon Trilogy. But that's beside the point. The passage seems to suggest that Strauss was able to threaten Durandal, and consequently Durandal was afraid of him. What was the threat? One of control? One of destruction? And why was Strauss the only individual able to intimidate Durandal in this way? Was he Durandal's creator? Had he discovered a secret Durandal had tried to keep hidden? Was it his knowledge of this secret that led to Durandal's shame, and his fear of Strauss? Much to think about.
Durandal fears Strauss. And Strauss apparently fears the cyborg player, as suggested on Nuke and Pave. Such a relationship seems to place Durandal a couple of "trophic levels" below us for once. The player seems to wield some kind of power over Strauss, and, vicariously, over Durandal himself...
Finally, one might wonder precisely how "Durandal learned Strauss was no longer a threat to him." Apparently Strauss is dead, so it may well be that Durandal saw his body through our eyes whilst we were aboard the Scoutship. (This would call into question the relationship between Durandal and the player, as the Story Page has done in the past. Are the two entities in some way "linked," such that Durandal can observe the world from inside the cyborg's head?) A thought that has often crossed my mind is that the dissected BOB hidden away in Marathon's Shapes file was originally intended as a representation of the dead Strauss. Allow me to explain: The Pfhor cyborg appeared only once in the game, and was thus easily recognisable as a unique individual to whom Durandal made specific reference. Perhaps the player was only meant to encounter the dismembered BOB once, and on a Pfhor level. The uniqueness of the encounter, (and the unpleasantness of the image itself,) would ensure that the event stood out in the player's mind. In a subsequent level Durandal would mention that he had seen Strauss' mutilated body aboard the ship, and the player would have been able to confirm the fact that Strauss was dead. Bungie's decision to keep the relationship between Strauss and Durandal more secretive may then have led to their rejection of this idea, so that Strauss' fate remained a mystery.
Finally, if Strauss is indeed dead, then how is it that "we haven't heard the end of this story?"
I hope these quotations prove useful. They certainly made me think when I first read them. But I appreciate that that was a long time ago now, and much research has been conducted since then. But even if what I've communicated here merely reiterates existing theories, then the official Bungie seal that accompanies this evidence should at least serve to lend those theories credence.
I am aware of your commendable belief is providing the readers of the Story Page with evidence of the sources referenced by the contributors. My University, imperfect as it is, is nevertheless equipped with a selection of (ageing) scanners, and I have a cursory knowledge of how to operate them. If you decide to include any of the above information on the page, then I'd be happy to provide you with a scanned image of the letter itself.
Thanks for letting me share my own little bit of successful research with other Marathon fans for the first time. I'm honoured to be able to contribute.