Tony followed Gibbs down the stairwell, both men hurrying as fast as they could without giving away their position to anyone listening for trouble. He had his gun out, pointed at the ground in front of him, as he followed at Gibbs’ six. As Gibbs slowly opened the stairwell door at the basement level, Tony stayed two steps up to peek over his shoulder. They could see the red emergency light was on in the hallway, but no lights inside Autopsy. If Ducky and Kate were in there alone the lights would have been on. By being off, they got confirmation that something was wrong.