: 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.
Note: while the rioters were armed, the fatal shot appears to have been fired by the troopers upon the protesters, not the other way around.
"As the UEG troopers approached the scene
in their Randal Hovertank, plasma fire began spraying upwards.
In a flash decision, the commander of the Hovertank ordered
his crew to open fire upon the crowd."
("The Rose", Terminal 2)
Though that doesn't rule out Strauss engineering the massacre. I figures that he always wanted Durandal to go rampant so that he could study rampancy and harness the power he thought he could acquire from controlling Durandal; forcing Durandal to be complicit in such a tragedy would definitely not be good for his emotional stability.
