“Any matches?”

“None. The difference was immediately apparent under the microscope. First, the red pigment granules in the pastel crayons showed far less variability in color and refractive index. That’s because most anhydrous iron oxide used in pigments today is synthetic-manufactured, not mined from the earth. They commonly use a compound called Mars Red, a mixture of iron and aluminum oxides.”

“So these pigment granules here, in this photo, aren’t synthetic?”

“No, this is naturally occurring anhydrous iron oxide. It’s also called hematite, derived from the Greek word for blood. Because it’s sometimes red.”

“Do they use the natural stuff in art supplies?”

“We did find a few specialty chalks and pastel crayons that use natural hematite as a pigment. But chalks contain calcium carbonate. And manufactured pastel crayons usually use a natural glue to bind the pigment. Some kind of starch, like methyl cellulose or gum tragacanth. It’s all mixed together into a paste, which is then extruded through a mold to make crayons. We found no traces of gum tragacanth or any binding starch in the crime-scene samples. Nor did we find enough calcium carbonate to indicate that this came from colored chalk.”

“Then we’re not dealing with something you’d find at an art supply store.”

“Not locally.”

“So where did this red stuff come from?”

“Well, let’s talk about this red stuff first. What it is, exactly.”

“You called it hematite.”

“Right. Anhydrous iron oxide. But when it’s found in tinted clay, it has another name as well: ocher.”

Frost said, “Isn’t that, like, what American Indians used to paint their faces?”

“Ocher has been used by mankind for at least three hundred thousand years. It’s even been found in Neanderthal graves. Red ocher in particular seems to have been universally valued in death ceremonies, probably because of its similarity to blood. It’s found in Stone Age cave paintings and on walls in Pompeii. It was used by the ancients to color their bodies as decoration or war paint. And it was used in magical rituals.”

“Including satanic ceremonies?”

“It’s the color of blood. Whatever your religion, that color has symbolic power.” Erin paused. “This killer makes quite unusual choices.”

“I think we already know that,” said Jane.

“What I mean is, he’s in touch with history. He doesn’t use common chalk for his ritual drawings. Instead he uses the same primitive pigment that was used in the Paleolithic era. And he didn’t just dig it up in his own backyard.”

“But you said that red ocher is found in common clay,” said Frost. “So maybe he did dig it up.”

“Not if his backyard is anywhere around here.” Erin nodded at the file folder Jane was holding. “Check out the chemical analysis. What we found on gas chromatography and Raman spectroscopy.”

Jane flipped to the next page and saw a computer printout. A graph with multiple spikes. “You want to interpret this for us?”

“Sure. First, the Raman spectroscopy.”

“Never heard of it.”

“It’s an archaeologist’s technique for analysis of historic artifacts. It uses the light spectrum of a substance to determine its properties. The big advantage for archaeologists is that it doesn’t destroy the artifact itself. You can analyze the pigments on everything from mummy wrappings to the Shroud of Turin and not damage the article in any way. I asked Dr. Ian MacAvoy, from the Harvard archaeology department, to analyze the Raman spectra results, and he confirmed that the sample contains iron oxide plus clay plus silica.”

“That’s red ocher?”

“Yes. Red ocher.”

“But you already knew that.”

“Still, it was nice to have him confirm it. Then Dr. MacAvoy offered to help me track down its source. Where in the world this particular red ocher came from.”

“You can actually do that?”

“The technique’s still in its research stages. It probably wouldn’t hold up in court as evidence. But he was curious enough to run a comparison against a library of ocher profiles he’s compiled from around the world. He determines the concentrations of eleven other elements in the samples, such as magnesium, titanium, and thorium. The theory is, a particular geographic source will have a distinctive trace element profile. It’s like looking at soil samples from a car tire and knowing that it has the lead-zinc profile of a mining district in Missouri. In this case, with this ocher, we’re checking the sample against eleven separate variables.”

“Those other trace elements.”

“Right. And archaeologists have compiled a library of ocher sources.”

“Why?”

“Because it helps determine the provenance of an artifact. For instance, where did the pigment on the Shroud of Turin come from? Was it France or Israel? The answer may establish the shroud’s origins. Or an ancient cave painting-where did the artist get his ocher? If it came from a thousand miles away, it tells you that either he’s traveled that distance himself, or that there was some form of prehistoric trade. That’s why the ocher source library is so valuable. It gives us a window into the lives of the ancients.”

“What do we know about our pigment sample?” asked Frost.

“Well.” Erin smiled. “First, it has rather a large proportion of manganese dioxide-fifteen percent, giving it a deeper, richer tone. It’s the same proportion found in red ochers that were used in medieval Italy.”

“It’s Italian?”

“No. The Venetians imported it from elsewhere. When Dr. MacAvoy compared the entire elemental profile, he found that it matched one location in particular, a place where they’re still mining red ocher even today. The island of Cyprus.”

Jane said, “I need to see a world map.”

Erin pointed to the file. “It just so happens that I pulled one off the Internet.”

Jane flipped to the page. “Okay, I see. It’s in the Mediterranean, just south of Turkey.”

“It seems to me that red chalk would’ve been a lot easier to use,” said Frost.

“And far cheaper. Your killer chose an unusual pigment, from an obscure source. Maybe he has ties to Cyprus.”

“Or he could just be playing games with us,” said Frost. “Drawing weird symbols. Using weird pigments. It’s like he wants to screw around with our heads.”

Jane was still studying the map. She thought of the symbol drawn on the door in Anthony Sansone’s garden. Udjat, the all-seeing eye. She looked at Frost. “Egypt is directly south of Cyprus.”

“You’re thinking of the eye of Horus?”

“What’s that?” Erin asked.

“That symbol left at the Beacon Hill crime scene,” said Jane. “Horus is the Egyptian sun god.”

“Is that a satanic symbol?”

“We don’t know what it means to this perp,” said Frost. “Everyone’s got a theory. He’s a Satanist. He’s a history buff. Or it could just be plain old-fashioned insanity.”

Erin nodded. “Like Son of Sam. I remember the police wasted a lot of time wondering who the mysterious Sam was. It turned out to be nothing more than the killer’s auditory hallucination. A talking dog.”

Jane closed the folder. “You know, I kind of hope our perp is crazy, too.”

“Why?” asked Erin.

“Because I’m a lot more scared of the alternative. That this killer is perfectly sane.”

Jane and Frost sat in the car as the engine warmed and the defroster melted the fog from the windshield. If only it was so easy to clear the mist cloaking the killer. She couldn’t form a picture of him; she couldn’t begin to imagine what he looked like. A mystic? An artist? An historian? All I do know is that he’s a butcher.

Frost shifted into gear, and they pulled into traffic, which was moving far more slowly than usual, on roads slick with ice. Under clear skies, the temperature was dropping, and tonight the cold would be the bitterest so far this winter. It was a night to stay home and eat a hearty stew, a night, she hoped, when evil would stay off the streets.