I drugged you both before kidnapping you, obviously, so there was no chance for you to fight back. Then I moved you both into the locked room, so it wasn't possible for you to use the weapons against me.
You would try to kill each other when I order you to, because you'd both know that if you don't, you'll have me to contend with and I will hurt you a lot more (before killing you) then either of you would do to each other.