The Bone Collector

it under the polarized-light ’scope. He adjusted dials.
    “Hmm. This is curious. No birefringence.”
    Polarizing microscopes show birefringence—the double refraction of crystals and fibers and some other materials. Seashore sand birefringes dramatically.
    “So it isn’t sand,” Rhyme muttered. “It’s something ground up. . . . Can you individuate it?”
    Individuation . . . The goal of the criminalist. Most physical evidence can be identified. But even if you know what it is there are usually hundreds or thousands of sources it might have come from. Individuated evidence is something that could have come from only one source or a very limited number of sources. A fingerprint, a DNA profile, a paint chip that fits into a missing spot on the perp’s car like a jigsaw-puzzle piece.
    “Maybe,” the tech responded, “if I can figure out what it is.”
    “Ground glass?” Rhyme suggested.
    Glass is essentially melted sand but the glassmaking process alters the crystalline structure. You don’t get birefringence with ground glass. Cooper examined the sample closely.
    “No, I don’t think it’s glass. I don’t know what it is. I wish I had an EDX here.”
    A popular crime lab tool was a scanning electron microscope married to an energy-dispersive X-ray unit; it determined what elements were in trace samples found at crime scenes.
    “Get him one,” Rhyme ordered Sellitto, then looked around the room. “We need more equipment. I want a vacuum metal fingerprint unit too. And a GC-MS.” A gas chromatograph broke down substances into their component elements, and mass photospectrometry used light to identify each one of them. These instruments let criminalists test an unknown sample as small as one millionth of a gram and compare it against a database of a hundred thousand known substances, cataloged by identity and name brand.
    Sellitto phoned the wish list in to the CSU lab.
    “But we can’t wait for the fancy toys, Mel. You’ll have to do it the old-fashioned way. Tell me more about our phony sand.”
    “It’s mixed with a little dirt. There’s loam, flecks ofquartz, feldspar and mica. But minimal leaf and decomposed-plant fragments. Flecks here of what could be bentonite.”
    “Bentonite.” Rhyme was pleased. “That’s a volcanic ash that builders use in slurry when they’re digging foundations in watery areas of the city where the bedrock’s deep. It prevents cave-ins. So we’re looking for a developed area that’s on or near the water, probably south of Thirty-fourth Street. North of that the bedrock’s much closer to the surface and they don’t need slurry.”
    Cooper moved the slide. “If I had to guess, I’d say this is mostly calcium. Wait, something fibrous here.”
    The knob turned and Rhyme would’ve paid anything to be looking through that eyepiece. Flashed back to all the evenings he’d spent with his face pressed against the gray sponge rubber, watching fibers or flecks of humus or blood cells or metal shavings swim into and out of focus.
    “Here’s something else. A larger granule. Three layers. One similar to horn, then two layers of calcium. Slightly different colors. The other one’s translucent.”
    “Three layers?” Rhyme spat out angrily. “Hell, it’s a seashell!” He felt furious with himself. He should have thought of that.
    “Yep, that’s it.” Cooper was nodding. “Oyster, I think.”
    The oyster beds around the city were mostly off the coasts of Long Island and New Jersey. Rhyme had hoped that the unsub would limit the geographic area of the search to Manhattan—where the victim that morning was found. He muttered, “If he’s opening up the whole metro area the search’ll be hopeless.”
    Cooper said, “I’m looking at something else. I think it’s lime. But very old. Granular.”
    “Concrete maybe?” Rhyme suggested.
    “Possibly. Yes.
    “I don’t get the shells then,” Cooper added reflectively. “Around New York the oyster beds’re full of vegetation and mud. This is mixed with concrete and there’s virtually no vegetable matter at all.”
    Rhyme barked suddenly. “Edges! What are the edges of the shell like, Mel?”
    The tech gazed into the eyepiece. “Fractured, not worn. This’s been pulverized by dry pressure. Not eroded by water.”
    Rhyme’s eyes slipped over the Randel map, scanning right and left. Focusing on the leaping dog’s rump.
    “Got it!” he cried.
    In 1913 F. W. Woolworth built the sixty-story