The bite marks are the reason for my involvement with the case. I’m a forensic odontologist, an expert on human teeth and the damage they can do. I acquired this knowledge in four boring years of dental school and five fascinating years of fieldwork. If people ask me what I do for a living, I tell them I’m a dentist, which is true enough and all they need to know. Odontologist doesn’t mean anything to anybody, but in post- CSI America, forensic prompts questions I’d just as soon not answer in a grocery store. So, while most acquaintances know me as a dentist who’s too busy to accept new patients, an assortment of government agencies-including the FBI and the United Nations Commission for the Investigation of War Crimes-knows me as one of the leading forensic odontologists in the world. Which is nice. I take my identity where I can find it.

The task force wants my expertise on bite marks tonight, but Sean Regan wants more. When he sought my help on a murder case two years ago, he soon learned that I knew about a lot more than teeth. I completed two years of medical school before I withdrew, and that gave me a strong foundation for self-education in forensics. Anatomy, hematology, histology, biochemistry, whatever a case requires. I can glean twice as much information from an autopsy report as any detective, and twice as fast. After Sean and I became closer than the rules allowed, he began using me unofficially to help with difficult cases. And used is the proper word; Sean Regan lives to catch killers, and he’ll exploit anything and anyone to help him do it.

But Sean isn’t simply a user. He’s my comrade-in-arms, my rabbi, and my enabler. He doesn’t judge me. He knows me for what I am, and he gives me what I need. Like Sean, I’m a born hunter. Not of animals. I’ve hunted animals, and I hate it. Animals are innocent; men are not. I am a hunter of men. But unlike Sean, I have no license to do this. Not really. Forensic odontology brings only tangential involvement with murder cases; it’s my involvement with Sean that puts me into the bloody thick of things. By allowing me access-unethical and probably illegal access-to crime scenes, witnesses, and evidence, he has put me in a position to solve four major murder cases, one of them a serial. Sean took the credit every time, of course-plus the attendant promotions-and I let him do it. Why? Maybe because telling the truth would have exposed our love affair, gotten Sean fired, and freed the killers. But the truth is simpler than that. The truth is that I didn’t care about the credit. I’d tasted the pulse-pounding rush of hunting predators, and I was addicted to it as surely as I am to the vodka I need so terribly at this moment.

For this reason, I’ve let our relationship run long past the point where I would usually have sabotaged it. Long enough, in fact, for me to have forgotten one of my hardest-won lessons: the husband doesn’t leave. Not the husbands I pick, anyway. Only this time it’s different. Sean has gone a long way toward convincing me he really means to do it. And I’m very close to believing him. Close enough to find myself hoping desperately for it in the most vulnerable hours of the night. But nowthe situation has changed. Fate has taken a hand. And unless Sean really surprises me, our relationship is over.

Without warning, a wave of nausea rolls through my stomach. I try to tell myself it’s alcohol withdrawal, but deep down I know better. It’s panic. Pure terror at the idea of giving up Sean and being alone. Don’t think about it, says a shaky voice inside me. In two minutes you’re onstage. Think about the case“¦

As I decelerate down the interstate ramp to the surface streets at St. Charles Avenue, my cell phone rings out the opening notes to U2’s “Sunday, Bloody Sunday.” I know without looking that it’s Sean.

“Where are you?” he asks.

I’m still fifteen blocks from the stately Victorian houses of Prytania Street, but I need to calm Sean down. “A few blocks from the scene.”

“Good. Can you handle your gear okay?”

My dental case weighs thirty-one pounds fully loaded, and tonight I’ll also need my camera case and tripod. Maybe Sean is hinting that I should ask him outside to help me. This would give him an excuse for a private talk before we find ourselves together in front of others. But a private talk is the last thing I want tonight.

“I’ve got it,” I tell him. “You sound strange. What’s going on down there?”

“Everybody’s uptight. You know the history.”

I do. There have been three serial murder cases in the New Orleans-Baton Rouge area in as many years, and serious investigative mistakes were made in all of them.

“We got some Sixth District detectives down here,” Sean goes on, “but the task force has taken over the scene. We’ll be running our investigation out of headquarters, just like the others. Captain Piazza’s already busting my balls.”

Carmen Piazza is a tough, fiftysomething Italian-American woman who came up through the ranks of the detective bureau and is now the Homicide Division commander. If anyone ever fires Sean for his involvement with me, it will be Piazza. She likes Sean’s record of arrests, but she thinks he’s a cowboy. And she’s right. He’s a tough, devilish Irish cowboy. “Does she suspect anything about us?”

“No.”

“No rumors? Nothing?”

“Don’t think so.”

“What about Joey?” I ask, referring to Sean’s partner, Detective Joey Guercio. “Has he blabbed to anybody?”

A millisecond’s hesitation. “No way. Look, just be cool like you always are. Except for last time. You feeling okay about that? Your nerves or whatever?”

I close my eyes. “I was until you asked.”

“Sorry. Just hurry down here. I’m going back in.”

A rush of anxiety blindsides me. “You can’t wait for me?”

“Probably better if I don’t.”

Better for you “¦”Fine.“

Focus on the case, I tell myself, checking the house numbers on Prytania to be sure where I am. They expect you to know your business.

The facts are simple enough. In the past thirty days, three men have been shot by the same gun, bitten by the same set of teeth, and-in two cases-marked by the saliva of a man whose DNA shows him 87 percent likely to be a Caucasian male. The NOPD crime lab did the ballistics that matched the bullets. The state police crime lab did the mitochondrial DNA match. And I matched the bite marks.

This is much more difficult than it appears to be on television. To explain my job to homicide detectives, I often tell them about the forensic researcher who used an articulated set of teeth to try to create perfectly matched bite marks on a corpse. He couldn’t do it. The lesson is clear, even to street cops. If matching two bite marks known to have come from the same set of teeth can be difficult, then matching marks that might have been made by any teeth among millions is next to impossible. Even comparing bite marks on a corpse with the teeth of a small group of suspects is more problematic than many odontologists pretend.

Saliva left in a bite mark by a killer can simplify things enormously, by providing DNA to compare against that of suspects. But four weeks ago, when the first victim was discovered, I recovered no saliva from the two bite marks on the body. I figured the killer for an organized offender who washed the saliva out of his bites to prevent recovery of DNA evidence. But a week later, when the second victim was found, my theory was blown out of the water. I recovered saliva from two of four bite marks left on the corpse. This raised the possibility of a different-and disorganized-killer. But by using reflective ultraviolet photography and scanning electron microscopy on the bite marks, I concluded that the same killer had indeed murdered both victims. Ballistic analysis of the recovered bullets supported my conclusion, and six days later, when the third victim was murdered, my opinion was confirmed beyond doubt by DNA recovered from the bite marks left on that body. The same killer had murdered all three men.