She laid four pictures on the table.

“Tell me what you see,” she said. I took her words to mean that class was in session.

I looked at the first picture. Alexandra Ruiz was a pretty girl, not that much older than me. You thought she was pretty, too. You watched her drown, but you didn’t hold her under. You didn’t leave any marks on her skin.

“It’s not about violence,” Dean said. “I never laid a hand on her. I never had to.”

I picked up where Dean left off. “It’s about power.”

“The power to predict what she would do,” he continued.

I concentrated. “The power to influence her. To knock over the first domino and watch the rest fall.”

“To do the math,” Dean filled in.

“What about the second victim?” Sterling asked. “Was it just math with him, too?”

I turned my attention to the second picture, the body burned beyond all recognition.

“I didn’t kill him,” Dean murmured. “I made it happen, but I didn’t strike the match. I watched.”

You spend a lot of time watching, I thought. You know how people operate, and you despise them for it. For thinking, even for a second, that they’re your equals.

“It’s not about overpowering people,” I said out loud, my eyes locking onto Dean’s. “It’s about outsmarting them.”

Dean bowed his head slightly, his eyes fixed on something none of us could see. “No one knows what I really am. They think they do, but they don’t.”

“It’s important,” I countered, “to show them. The numbers, the pattern, the planning—you want them to see.”

“Who?” Agent Sterling prompted. “Whose attention is the UNSUB trying to get?” I could tell by the tone in her voice that she’d asked herself that question. The fact that she was also asking us told me something about the answer.

“Not just the FBI,” I said slowly. “Not just the police.”

Sterling tilted her head to the side. “Are you telling me what you think I want to hear, or are you telling me what your gut is saying?”

The numbers mattered to the UNSUB. They matter to you, because they matter to someone else. I’d thought that the UNSUB was performing. For who?

I answered Sterling’s question. “Both.”

Sterling gave a brief nod and then tapped her fingers against the third photo.

“The arrow,” Dean said. “No more dominoes. I pulled the trigger myself.”

“Why?” Sterling pushed us. “Power, influence, manipulation—and then blunt force? How does a killer make that transition? Why does a killer make that transition?”

I stared at the picture, willing myself to see the UNSUB’s logic. “The message on the arrow,” I said. “Tertium. For the third time. In your mind, they’re all the same—drowning and watching someone burn alive and shooting the old man with an arrow, they’re the same thing to you.”

But they’re not. That was what I couldn’t shake. The manner in which an UNSUB killed told a story about motivations and underlying psychological needs.

What story are you telling me?

“Camille Holt was strangled with her own necklace.” Dean moved on to the final picture. “Organized killers typically bring their own weapons to the scene.”

“Yes,” Agent Sterling replied, “they do.”

Strangling was personal. It was physical, far more about dominance than manipulation.

“You carved the numbers into her skin,” I said out loud. “To punish her. To punish yourself for falling short of perfection.”

You have a plan. Failure is not an option.

“What’s the trajectory here?” Agent Sterling prompted.

“More violent with each kill,” Dean said. “And more personal. He’s escalating.”

Agent Sterling gave a brief nod. “Escalation,” she said, falling into lecture mode, “happens as a killer begins needing more with each kill. It can manifest in any number of ways. A killer who starts by stabbing victims once and then switches to stabbing them over and over is escalating. A killer who starts by killing once a week and then kills two victims in the same day is escalating. A killer who starts out targeting people who are easy to pick off and graduates to harder and harder targets is escalating.”

“And,” Dean added, “a killer who moves on to progressively more violent means with each subsequent kill is escalating.”

I saw the logic inherent in what they were saying. “Diminished returns,” I said. “Like a junkie shooting up and needing progressively stronger doses to get the same high each time.”

“Sometimes,” Agent Sterling agreed. “Other times, escalation can reflect a loss of control, brought on by some kind of external stressor. Or it might reflect a killer’s growing belief that he’s invulnerable. As the UNSUB becomes more grandiose, so do the kills.”

You’re escalating. I meditated on that for a moment. Why?

I spoke the next question to cross my mind out loud. “If the UNSUB is escalating,” I said, “why would he stop?”

“He couldn’t.” Dean’s voice was flat.

Four bodies in four days, and then nothing.

“Most serial killers don’t just stop,” Agent Sterling said. “Not unless someone or something stops them.”

The way she said those words told me she was thinking about another case—about a particular killer she’d hunted once who had stopped. The one who got away.