I am at the point where I'm dong the "Thief Assignment." I start on a roof and need to use the thiefs to lure the guards away from the chest. How do I do that? As soon as we go over by the guards, the thiefs rob all the citizens but the guards stay put. I can get them fighting but as soon as a guard dies then it ends. It's not clear on how to get the thiefs to do anything here.