The last time Nathan had been in the basement for any kind of interrogation, it was with this very same individual and it had been to keep Peter from killing her outright for her part in Faith's torment. So he knew her tricks, which was why Peter's attention was currently diverted to maintaining the structural integrity of the room, as well as blocking the sounds from the rest of the building, and, of course, the temperature. It was cool, but they were all prepared by being dressed for it. That was, all except their new prisoner.
"Do whatever you need to do, but don't kill her," he said to Jacen, then moved to the side of the room to observe. For Nathan, there was still a difference between killing on the battlefield, in the middle of a fight, and killing what had already been trapped and rendered mostly incapacitated. Given he'd had his fill of Azula the last time, letting Jacen utilize his skills was no doubt good for both effectiveness and Nathan's demeanor.