Christine felt her stomach turn over, and it wasn’t only the graphic nature of what he was saying. Zachary seemed to go into loving detail about the human anatomy. “I would think that would be difficult to hear about at dinner, much less see.”

“No, I could compartmentalize it. When she showed me the cadavers, they were all lined up in steel boxes and each had an index card with their occupation, cause of death, and age taped to their case. She didn’t even know how to put the scalpel blade on the shaft, I had to show her.”

“How did you know?”

“From work. I know all about scalpels. Brigham makes thirty-seven different types, at three different product lines and price points.” Zachary nodded. “For the first slice into the flesh, and depending on where the flesh is or how thick, you use a different scalpel. I won’t bore you with details, it’s shop talk. But once you pierce the skin, the scalpel should glide with ease until you hit a bony structure or muscle, with the exception of the face. You really have to peel that, and fat is yellow and greasy, almost like a really ripe mango.”

“Yuck,” Christine heard herself say before she could stop herself. She understood that a prospective medical student would revel in the details of human anatomy, but Zachary was sending shivers up her spine. Lauren must have felt the same way because she leaned away from him.

“Sorry you asked?” Zachary smiled, warming to his topic. “My girlfriend showed me her notes, and the professor said that the trick to anatomy is finding the right fascial plane, the layer of fascia where you could freely separate the muscles from one another or from a structure. My girlfriend said, finding a good plane could be the difference between a two-hour dissection and a four-hour dissection that she had to superglue together.”

“Superglue?” Christine asked, thinking she had misheard him.

“Yes, everyone in med school stashes superglue in their table.” Zachary chuckled in a knowing way. “It’s inevitable you’ll rip a nerve when you’re moving a muscle out of the way, or working too fast with your scalpel down a fascial plane. A little bit of superglue, and the nerve will innervate the muscle again.” Zachary leaned back, relaxing. “You know what I’d love most of all? Heart dissection. It’s probably the coolest of all. I’d have loved to be in cardiology research.”

“Why?” Christine asked, shocked. She was remembering the detail about Gail Robinbrecht’s murder and the other nurses, killed with a single stab wound to the left ventricle. She didn’t understand why Zachary would even go there, given that he must have read the same accounts, but she didn’t stop him. She wrote a note, cardiology, so he couldn’t see her expression.

“You cut the rib cage open to get into the thorax, then go through the pericardial sac, which the heart sits inside of.” Zachary made a cutting motion with his hand, demonstrating by holding an imaginary scalpel. “You cut one major vessel at a time—coronaries, aorta, pulmonary vein—and once you’ve cut all of the connecting structures, you deliver the heart from the pericardial sac.” Zachary paused, his smile spreading. “And then you’re holding a human heart in your hands.”

“How do you know this?” Christine asked, horrified. “Did your girlfriend tell you?”

“Yes, and then I got to observe heart surgery in the hospital. The surgeons let me, and my boss came, too. We had to see how the instruments performed in the OR. The most surprising thing? The heart is small. It seems so small to have such a huge role in your life, it’s smaller than your liver and your lungs by a lot.” Zachary’s blue eyes lit up. “You examine the outside and the four chambers, and how they circulate from the body to right atrium, then to the right ventricle, via the tricuspid valve.” Zachary made a loop de loop with his hands, in the air. “Then to the pulmonary artery and lungs, then back via the pulmonary vein to the left atrium and to the left ventricle, via the mitral or bicuspid valve. The left ventricle is the powerhouse. It pumps to the entire body’s systemic circuit, via the aorta.”

Christine couldn’t take it any longer. “You know, that’s the way Gail Robinbrecht was murdered, the way they all were murdered, stabbed in the left ventricle.”

“I’m aware, and the newspapers say the killer must have been a doctor or a med student, but if he was, he wasn’t a very good one.” Zachary’s tone turned superior. “It’s true that you can kill somebody by stabbing the left ventricle, but that takes a lot of force. The heart is tucked in under the lungs, and the left ventricle is the bottom right, here, called the ‘apex of the heart.’” Zachary pointed at his chest. “The killer would have to aim between the second and fifth intercostal space, between the ribs on the left side, then angle it up and in to reach the apex of the heart.”

Christine kept her expression impassive, but Zachary continued, oblivious.

“The intercostal spaces are only an inch or two between each rib, that’s why it would be hard to have perfect aim with the first stab, without getting stopped by a rib. That’s why your ribs are there, after all, to protect your thorax and mediastinum.” Zachary’s eyes lit up. “The human body is a beautiful thing, the way it’s designed, all of it intended to protect the heart, to keep the person alive. So obviously, you could kill somebody that way, but it doesn’t make sense.” Zachary shrugged. “That’s how you know I’m innocent. I know better than this serial killer. If I wanted to kill somebody with a stab wound, I would stab the carotid, or the second-best, the right kidney. It’s above the right hip, lower than the left kidney. If you stab somebody there, that would send them into shock, and they’d bleed out and die.”

Christine flip-flopped, changing her mind. Zachary might have known about anatomy, but maybe he truly was innocent. He seemed to be saying that someone who knew about anatomy wouldn’t have killed the nurses the way they’d been killed, meaning he was innocent.

“The other problem with stabbing someone in the left ventricle, or anywhere in the heart, is that the heart is so strong it will initially try to contract to hold the gap closed, but the more wide and gaping the stab wound to the heart wall, the more blood will leak out. It would pump out of the chest with each heart beat after the stabbing.”

Christine recoiled.