The Empty Chair

the riverbank,” Sachs pointed out. “Maybe he had another boat hidden up- or downstream.”
    “That’s true,” Jesse said, earning a dark glance from Lucy.
    A long moment of silence, the four people standing immobile while gnats strafed them and they sweated in the merciless heat.
    Finally Sachs said simply, “We’ll wait.”
    Sealing the decision, she sat on what was surely the most uncomfortable rock in the entire woods and, with feigned interest, studied a woodpecker drilling fiercely into a tall oak in front of them.

. . . chapter nine
    “Primary scene first,” Rhyme called to Ben. “Blackwater.”
    He nodded at the cluster of evidence on the fiberboard table. “Let’s do Garrett’s running shoe first. The one he dropped when he snatched Lydia.”
    Ben picked it up, unzipped the plastic bag, started to reach inside.
    “Gloves!” Rhyme ordered. “Always wear latex gloves when handling evidence.”
    “Because of fingerprints?” the zoologist asked, hurriedly pulling them on.
    “That’s one reason. The other’s contamination. We don’t want to confuse places you’ve been with places the perp has been.”
    “Sure. Right.” Ben nodded his massive crew-cut head aggressively, as if he were fearful of forgetting this rule. He shook the shoe, peered into it. “Looks like there’s gravel or something inside.”
    “Hell, I didn’t have Amelia ask for sterile examining boards.” Rhyme looked around the room. “See that magazine there? People ?”
    Ben picked it up. Shook his head. “It’s three weeks old.”
    “I don’t care how current the stories about Leonardo DiCaprio’s love life are,” Rhyme muttered. “Pull out the subscription inserts inside. . . . Don’t you hate those things? But they’re good for us—they come off the printing press nice and sterile, so they make good mini–examining boards.”
    Ben did as instructed and poured the dirt and stones onto the card.
    “Put a sample in the microscope and let me take a look at it.” Rhyme wheeled close to the table but the ocular piece was a few inches too high for him. “Damn.”
    Ben assessed the problem. “Maybe I could hold it for you to look in.”
    Rhyme gave a faint laugh. “It weighs close to thirty pounds. No, we’ll have to find a—”
    But the zoologist picked up the instrument and, with his massive arms, held the ’scope very steady. Rhyme couldn’t, of course, turn the focusing knobs but he saw enough to give him an idea of what the evidence was. “Limestone chips and dust. Would that’ve come from Blackwater Landing?”
    “Uhm,” Ben said slowly, “doubt it. Mostly just mud and stuff.”
    “Run a sample of it through the chromatograph. I want to see what else is in there.”
    Ben mounted the sample inside and pressed the test button.
    Chromatography is a criminalist’s dream tool. Developed just after the turn of the century by a Russian botanist though not much used until the 1930s, the device analyzes compounds such as foods, drugs, blood and trace elements and isolates the pure elements in them. There are a half-dozen variations on the process but the most common type used in forensic science is the gas chromatograph, which burns a sample of evidence. Theresulting vapors are then separated to indicate the component substances that make up the sample. In a forensic science lab the chromatograph is usually connected to a mass spectrometer, which can identify many of the substances specifically.
    The gas chromatograph will only work with materials that can be vaporized—burned—at relatively low temperatures. The limestone wouldn’t ignite, of course. But Rhyme wasn’t interested in the rock; he was interested in what trace materials had adhered to the dirt and gravel. This would narrow down more specifically the places Garrett had been.
    “It’ll take a little while,” Rhyme said. “While we’re waiting let’s look at the dirt in the treads of Garrett’s shoe. I tell you, Ben, I love treads. Shoes, and tires too. They’re like sponges. Remember that.”
    “Yessir. I will, sir.”
    “Dig some out and let’s see if it comes from someplace different from Blackwater Landing.”
    Ben scraped the dirt onto another subscription card, which he held in front of Rhyme, who examined it carefully. As a forensic scientist, he knew the importance of dirt. It sticks to clothes, it leaves trails like Hansel’s and Gretel’s bread crumbs to and from a perp’s house and it links criminal and