Well I'm not sure what you want exactly, but this might help you. My theory worked as I thought it was (It's actually very basic).
Download a quick example of this here:
http://www.angelfire.com/clone/shadow6/mission.sqmPut it in a folder called 'Example.abel' under Codemasters > Operation Flashpoint > Users > <One of your user names> > missions.
If you don't kill the western soldier yourself, the civilian cop will. Your squad leader can't kill the western soldier because he's unarmed, and the western soldier can't attack any of the three of you because he's not armed either.
Now there are ways to twist this around if you want to mess around with different sides, but it can be pretty hard to fit the particular situation though. Just remember to set each side captive during the change.