the Imperium knew all along that the [mysterious substance] was hidden on AS431. somehow, (a) Marcus figured that out, and (b) the lord-generals figured out what the “Hareti” were. (interestingly enough, they didn’t see fit to inform their king-emperor.) all of the exploration and scientific work on the planet was driven by the desire to eventually control the planet, knowing that the efforts to extract [m.s.] would be too obvious to be hidden under the usual fictions (Haret, etc.). Marcus keeps a log of things, as he figures it out, using pen and paper. Which is what the investigators are actually looking for, under the guise of investigating the Aila incident. Because, of course, Marcus is actually part of the “resistance” – which comes back in II, with Saithe’s disdain for Marcus & vice versa. Marcus instructs Aila first to hide the log when he leaves the 2nd time, then gives it to her when she goes to Ult. (Why doesn’t she just read it? – because it’s written in code, perhaps his own invented language? which she might decipher, over time.)
All of which should be woven gently thru the story, w/out being heavy-handed. (yipes.) But I do think this is the missing element.