From Inside the Grey House:
Vincent pulled Natalia out into the hall, yelling his frustrations. He had no idea why she killed the Slayer, and had no idea why that disturbed look was on her face. It was as if her one and only hope had been torn from her very soul. Mierka was in the cell, feeling for the Slayer’s pulse. If there was any indication of life, she could turn him and they could continue to question him. When Mierka shook her head and looked over, Vincent bared his teeth and snarled.
“Natalia. Natalia! Snap out of it. What did he do?” His voice was a cacophony of annoyance, frustration and concern. He was trying to be gentle, but the main Slayer was dead and Mierka had informed him that the other two could not talk. He needed to know what happened in the cell. The microphones hadn’t picked anything up; they had spoken too quietly.