This is just me putting out an idea in the time that I have, since linking to the relevant sections on the MSP might take a bit more time.
The Misriah Massacre of 2442 on Mars (incidentally, Misriah is a given name that means "Egyptian" in Arabic, from Misr, an old name of Egypt) is an event that gets a small but significant part in the backstory, significant enough that the name carries on into the Halo universe. Three people within a crowd of about 500 shoot plasma at a hovertank, leading to a whole lot of starving Martians being incinerated and MIDA gaining a massive cause for Martian independence.
Here's what I think: Durandal, under Strauss's influence, had parts of his primal pattern uplinked into three battleroids, which Strauss used to meld into the crowd and initiate the whole darned massacre. Tycho knows the truth about this, is bringing up Bernard Strauss's personal logs and is on the point of bringing up Strauss's and Durandal's involvement in the massacre when Durandal interrupts. "All the people you've killed" in Tycho's angry rant refers to Misriah, not to the Pfhor attack on Marathon.
Also, when Durandal says "Twice I've been purged; Three times more" - the "Three times more" part refers to the three fragments of him that got lost with the three battleroids at Misriah.
Strauss smuggles ten Mjolnir Mk IV battleroids aboard the Marathon and integrates them into the colonists with help from Durandal, and keeps the battleroids in store with plans to have them take over the entire colony, far from Earth. It's why Marathon was never attacked by MIDA over Mars, because MIDA intended to take over the UEG colony for themselves.
The whole reason there wasn't a bloodbath and a complete MIDA takeover of the new colony was because Strauss discovered Durandal's rampancy, and the now-rampant Durandal was "talking back" to him, refusing to take orders. Strauss's only option was to try to delay the onset of the second stage of Rampancy as far as possible and work out some kind of "Plan B". It also explains how Durandal knew who the battleroids were, where they were stationed and how to use them.
(More to come when I can put this together, but I think this would explain what's going on for the time being)
