I’m calling the dead man Kerensky for the time being, on account of my just finishing John Scalzi’s Redshirts a couple of days ago. Miles Kerensky, who was—for the last year or so of his life—working as a surveyor on the lunar surface for some sort of organization that would have earned him a big enough suspect pool to keep things interesting.
Dead men always need layers in these kinds of books. Flaws and hobbies and psychological bright points enough to carry on through a couple of hundred pages of someone trying to figure out who would try to kill them and why. Things that keep them interesting and important even though we never meet them alive.
So, what’s up with Kerensky? Everyone is off of Earth for a reason, but, for the sake of the suspect pool, his should be a bit nastier and auspicious, rather than pure. Let’s say gambling debts and a nasty divorce drove him off-world…One of those things can at least chase him to the moon or crop up again there. Beyond that, there’s a good opportunity to involve him with an organization that can be important to plot and setting. A non-profit. Say, a lunar historical preservation society. Something that can put him on the wrong side of the corporations that are becoming more and more prolific in orbit, and provide him with an overbearing but socially popular boss and an ambition and cuthroat assistant/underling who might just be a bit of a femme-fatale.
It also couldn’t hurt to give him a hobby or two; just for flavor. Make him a junior astronomy buff or something like that.