“I’ll put up the lateral view,” said O’Donnell, and she slid a second X-ray onto the box. “Do you see it now?”

The second film showed the skull in profile. Rizzoli could now see a fine web of fracture lines radiating backward from the front of the cranium. She pointed to them.

O’Donnell nodded. “He was unconscious when they brought him into the E.R. A CT scan showed hemorrhaging, with a large subdural hematoma-a collection of blood-pressing on the frontal lobes of his brain. The blood was surgically drained, and he went on to recover. Or rather, he appeared to recover. He went home and eventually returned to work. But he was not the same man. Again and again, he lost his temper on the job and was fired. He began to sexually molest his daughter. Then, after an argument with his wife, he beat her so brutally her corpse was unrecognizable. He started pounding and he couldn’t stop. Even after he’d shattered most of her teeth. Even when her face was reduced to nothing but pulp and bone fragments.”

“You’re going to tell me it can all be blamed on that?” said Rizzoli, pointing to the fractured skull.

“Yes.”

“Give me a break.”

“Look at that film, Detective. See where the fracture is located? Consider which part of the brain lies right beneath it.” She turned and looked at Dean.

He met her gaze without expression. “The frontal lobes,” he said.

A faint smile twitched on O’Donnell’s lips. Clearly she enjoyed the chance to challenge an old rival.

Rizzoli said, “What’s the point of this X ray?”

“I was called in by the man’s defense attorney to perform a neuropsychiatric evaluation. I used what we call the Wisconsin Card Sort Test and a Category Test from the Halstead-Reitan Battery. I also ordered an MRI- magnetic resonance imaging-scan of his brain. All of them pointed to the same conclusion: This man suffered severe damage to both his frontal lobes.”

“Yet you said he fully recovered from the injury.”

“He appeared to recover.”

“Was he brain-damaged or wasn’t he?”

“Even with extensive damage to the frontal lobes, you can still walk and talk and perform daily functions. You could have a conversation with someone who’s had a frontal lobotomy and you might not detect anything wrong. But he is most certainly damaged.” She pointed to the X-ray. “What this man has is called frontal disinhibition syndrome. The frontal lobes affect our foresight and judgment. Our ability to control inappropriate impulses. If they’re damaged, you become socially disinhibited. You display inappropriate behavior, without any feelings of guilt or emotional pain. You lose the ability to control your violent impulses. And we all have them, those moments of rage, when we want to strike back. Ram our car into someone who’s cut us off in traffic. I’m sure you know what it feels like, Detective. To be so angry you want to hurt someone.”

Rizzoli said nothing, silenced by the truth of O’Donnell’s words.

“Society thinks of violent acts as manifestations of evil or immorality. We’re told we have ultimate control over our own behavior, that each and every one of us has the free will to choose not to hurt another human being. But it’s not just morality that guides us. Biology does as well. Our frontal lobes help us integrate thoughts and actions. They help us weigh the consequences of those actions. Without such control, we’d give in to every wild impulse. That’s what happened to this man. He lost the ability to control his behavior. He had sexual feelings toward his daughter, so he molested her. His wife made him angry, so he beat her to death. From time to time, we all have disturbing or inappropriate thoughts, however fleeting. We see an attractive stranger, and sex flashes into our heads. That’s all it is-just a brief thought. But what if we gave in to the impulse? What if we couldn’t stop ourselves? That sexual impulse could lead to rape. Or worse.”

“And that was his defense? ‘My brain made me do it’?”

Annoyance sparked in O’Donnell’s eyes. “Frontal disinhibition syndrome is an accepted diagnosis among neurologists.”

“Yeah, but did it work in court?”

A cold pause. “Our legal system is still working with a nineteenth-century definition of insanity. Is it any wonder the courts are ignorant of neurology as well? This man is now on death row in Oklahoma.” Grimly O’Donnell jerked the films from the light box and slid them into the envelope.

“What does this have to do with Warren Hoyt?”

O’Donnell crossed to her desk, picked up another X-ray envelope and withdrew a new pair of films, which she clipped onto the light box. It was another set of skull films, a frontal and lateral view, but smaller. A child’s skull.

“This boy fell while climbing a fence,” said O’Donnell. “He landed facedown, hitting his head on pavement. Look here, on this frontal view. You can see a tiny crack, running upward about the level of his left eyebrow. A fracture.”

“I see it,” said Rizzoli.

“Look at the patient’s name.”

Rizzoli focused on the small square at the edge of the film, containing identifying data. What she saw made her go very still.

“He was ten years old at the time of the injury,” said O’Donnell. “A normal, active boy growing up in a wealthy Houston suburb. At least, that’s what his pediatric records indicate, and what his elementary school reported. A healthy child, above-average intelligence. Played well with others.”

“Until he grew up and started killing them.”

“Yes, but why did Warren start killing?” O’Donnell pointed to the films. “This injury could be a factor.”

“Hey, I fell off a jungle gym when I was seven. Whacked my head against one of the bars. I’m not out there slicing people.”

“Yet you do hunt humans. Just as he does. You are, in fact, a professional hunter.”

Rage blasted Rizzoli’s face with heat. “How can you compare me to him?”

“I’m not, Detective. But consider what you’re feeling right now. You’d probably like to slap me, wouldn’t you? So what’s stopping you? What is it that holds you back? Is it morality? Good manners? Or is it just cool logic, informing you that there’ll be consequences? The certainty that you’ll be arrested? All these considerations together keep you from assaulting me. And it’s in your frontal lobes where this mental processing takes place. Thanks to those intact neurons, you’re able to control your destructive impulses.” O’Donnell paused. And added with a knowing look, “Most of the time.”

Those last words, aimed like a spear, found their mark. It was a tender point of vulnerability. Only a year ago, during the Surgeon investigation, Rizzoli had made a terrible mistake that would forever shame her. In the heat of a chase, she had shot and killed an unarmed man. She stared back at O’Donnell and saw the glint of satisfaction in the other woman’s eyes.

Dean broke the silence. “You told us Hoyt was the one who contacted you. What was he hoping to gain by all this? Attention? Sympathy?”

“How about plain human understanding?” said O’Donnell.

“Is that all he asked from you?”

“Warren is struggling for answers. He doesn’t know what drives him to kill. He does know he’s different. And he wants to know why.”

“He actually told you this?”

O’Donnell went to her desk and picked up a file folder. “I have his letters here. And the videotape of our interview.”

“You went to Souza-Baranowski?”

“Yes.”

“At whose suggestion?”

O’Donnell hesitated. “We both thought it would be helpful.”

“But who actually brought up the idea of a meeting?”

It was Rizzoli who answered the question for O’Donnell. “He did. Didn’t he? Hoyt asked for the meeting.”

“It may have been his suggestion. But we both wanted to do it.”

“You don’t have the faintest idea why he really asked you there,” said Rizzoli. “Do you?”