Hey sounds like a good idea but as has everyone else i spotted a few flaws.
Ok flaw number one, if your soldier shoots a civvy on a mission, sure its murder, but there will be an investigation, ect, and he wont get the armoury post....however if he doesnt get the armoury post he isnt going to know about the conspiracy, and is just gonna get court marshalled or something...in which case there is no action.
Two, even if his mates find out, how do they find out?
Three, its easier to kill someone than to frame them in a combat situation....in combat, its chaos, its hard to tell whos doing what....so the framing would be hard to make definate....however, if one of the soldiers were to pick up an enemy weapon.....
Anyway, i think it'd make far more sense to frame him as a murderer outside of an op....still have an intro op, maybe where you get told your promoted for your actions, or maybe even you screw up the op and get reassigned to a non combat post for your sins (like the anti-hero theme?), ie the armoury. Assuming that your a bum soldier because of this, they hint about you to join their scheme...when you go to turn them in...ok imm stopping i got a good twist and i dont want it broadcast...ill PM it