“The tests,” he said, “aren’t any big deal, they just examine phenomena mathematically. As in the likelihood of something happening by chance. One way to do that particular analysis is to draw comparisons between groups by examining the distribution of… the pattern of the scores. I did exactly that. Compared June 28 with every other day of the year. You’re right about homicides clustering, but no other date presents this pattern. Even summer effects tend to manifest on weekends or holidays. These six cases fall on various days of the week. In fact, only one- the first murder- took place on a weekend.”

Petra reached for her mug. Her tea had gone cold but she drank it anyway.

“Would you like some water?” said Isaac.

“I’m fine. What else?”

“Okay… another way to look at it, is to simply examine inherent base probabilities- ” He’d punctuated his words with index-finger jabs. Now he stopped, blushed even more intensely. “There I go again.” Another long, deep inhalation. “Let’s take it issue by issue. Start with weapon of choice, because that’s a discreet- It’s a fairly simple variable. Firearms are the clear favorite of L.A. murderers. I’ve looked at twenty years’ worth of one eighty-sevens and seventy-three percent have been carried out with handguns, rifles, or shotguns. Knives and other sharp objects are next, at around fifteen percent. That means those two modalities account for nearly ninety percent of all local murders. The FBI’s national figures are similar. Sixty-seven percent firearms, fourteen percent knives. Personal weapons- fists, feet- account for six percent and the rest is a mixed bag. So the fact that neither a gun nor a knife was used on any of the June 28 cases is notable. As is the nature of the fatal injury. In every data bank I’ve checked, blunt force homicides never rise above the level of five percent. They’re a rare occurrence, Detective Connor. I’m sure you know that better than I.”

“Isaac, I just closed two cases. A bare-fist blow to the head and a broken neck via martial arts.”

He frowned. “Then you just closed two rare ones. Have you seen many others?”

Petra thought back. She shook her head. “Not for a while.”

Isaac said, “If we get even more specific, cranial bludgeoning by unknown weapon accounts for no more than three percent of L.A. homicides. But it makes up one hundred percent of these cases. When you add the other similarities- identical calendar date, same approximate time, probable stranger homicides, and look at the probability of a chance cluster, you’re moving way past coincidence.”

He stopped.

Petra said, “That it?”

“Actually, there is a bit more. LAPD homicide detectives solve between two-thirds and three-quarters of their cases, yet all these cases remain unsolved.”

“That’s because they’re stranger homicides,” said Petra. “You’ve been here long enough to see the kind of stuff we clear quickly. Some moron holding the smoking gun when the uniforms get there.”

“I think you’re selling yourself short, Detective Connor.” Saying it sincerely, not a trace of patronizing. “The truth is you people are very effective- imagine a major league slugger hitting seven hundred. Even stranger homicides get solved. But not one of these. All that supports my thesis: these are highly irregular events. The final incongruity is that during the same six-year period, gang homicides rose from twenty percent of all homicides to nearly forty. Meaning the chance of a nongang murder lowered proportionately. Yet not one of the June 28 cases appear gang-related. Add all that up and we’re talking a combination of highly unusual circumstances. The likelihood of it boiling down to chance is one over so many zeros I don’t have a name for it.”

Bet you do, thought Petra. Bet you’re going easy on me.

She slid the list out from under his hand, took a closer look.

June 28 Homicides: An Embedded Pattern?

1. 1997: 12:12 a.m. Marta Doebbler, 29, Sherman Oaks, married white female. Out with friends at Pantages Theater in H’wood, went to ladies’ room, never returned. Found in own car, backseat, depressed skull fracture.

2. 1998: 12:06 a.m. Geraldo Luis Solis, 63, widowed Hispanic male. Found in his house, breakfast room, Wilsh. Div, food taken but no money, depressed skull fracture.

3. 1999: 12:45 a.m. Coral Laurine Langdon, 52, single white female, walked her dog in H’wood Hills, found by patrol car, under brush, six blocks from home. Depressed skull fracture. Dog (“Brandy,” 10 y.o. cockapoo) stomped to death.

4. 2000: 12:56 a.m. Darren Ares Hochenbrenner, 19, single black male, Navy ensign, stationed in Port Hueneme, on shore leave H’wood, found in alley, Fourth Street, Cent. Div, pockets emptied. Depressed skull fracture.

5. 2001: 12:01 a.m. Jewell Janis Blank, 14, single white female, runaway, found in Griffith Park, near Fern Dell, by rangers. Depressed skull fracture.

6. 2002: 12:28 a.m. Curtis Marc Hoffey, 20, single white male, known gay hustler, found in alley, Highland near Sunset. Depressed skull fracture.

Petra looked up. “There doesn’t seem to be any pattern victim-wise.”

“I know,” said Isaac, “but still.”

“I have a friend, a psychologist, who says people are walking prisms. We see with our brains, not our eyes. And what we see depends on context.”

Now she was pontificating. Isaac sat back. He looked crushed.

“My point is,” she said, “that it all depends on how you look at it. You’ve raised some interesting points- more than interesting… provocative.” She pointed to the list, ran her finger down the names. “These people are all over the place in terms of sex, age… social class. We’ve got urban and semirural dumpsites. If this is some kind of serial thing, there’d most likely be a sexual angle, and I can’t see what a sixty-three-year-old man and a fourteen-year-old girl would have in common as sexual targets.”

“All that’s true,” said Isaac. “But don’t you think the other factors are too blatant to be ignored?”

Petra’s head began hurting. “You’ve obviously put a lot of time into this and I’m not dismissing it, but- ”

“Why,” he interrupted, “does there have to be a sexual angle?”

“That’s the way it tends to shake out.”

“The FBI profile. Yes, yes, I know about all of that. Their basic thesis is that what they call organized killers- really just a dumbed-down version of what psychologists call psychopaths- are motivated by a combination of sexuality and violence. I’m sure that typically there’s some truth to that. But as you said, Detective, reality depends on which prism you’re using. The FBI interviewed imprisoned killers and compiled data banks. But data are only as good as the sample, and who says killers who get caught are similar to those who don’t? Maybe the FBI’s bad guys got caught because they were psychologically rigid. Maybe it was their predictability that tripped them up.”

His voice had climbed. Heat in the brown eyes made them something quite other than liquid. “All I’m saying is that sometimes exceptions are more important than rules.”

“What motive are you proposing for these killings?” said Petra.

Long pause. “I don’t know.”

Neither of them spoke. Isaac slumped. “Okay, thanks for your time.” He scooped up the list and stashed it in the shiny brown briefcase he carried around. Petra had seen detectives smile disparagingly at the case. She’d heard the comments behind Isaac’s back. Brainiac. Boy wonder. Petra’s little day-care project. When she felt assertive, she silenced the noise with an icy stare.

Now she found herself feeling protective of the kid but annoyed. The last thing she needed was some theory that got her dredging up six years of cold cases. Not with four victims down at the Paradiso, one of them a girl she couldn’t even identify.

On the other hand, Isaac was smarter than she was, much smarter. Dismissing him out of hand could turn out to be one of those big mistakes. And what if he went over her head to Schoelkopf- to Councilman Reyes. If that happened and he turned out to be right…