Not trying to market my work, but in this Armed Assault MP mission you will find a method that works quite well:http://www.ofpec.com/missions_depot/index.php?action=details&id=204
Script that senses if you are firing your weapon while detected.
Script that senses if an enemy have found a dead friend.
Script that by random can make an enemy suspect you (though setCaptive) and act accordingly, questioning etc.
I can explain better later if you are interested, I'm in a hurry now.