"Got some shoes," Sachs said, lifting a bag out of a cardboard box.

"His?"

"Probably. They're the same Ecco brand we found at the music school—same size, too."

"He left 'em behind. Why?" Sellitto wondered.

Rhyme suggested, "Probably thought that we knew he was wearing Eccos at the first scene and was worried the respondings'd noticed them on an elderly woman."

Examining the shoes, Mel Cooper said, "We've got some good trace in the indentation in front of the heel and between the upper and sole." He opened a bag and scraped the material out. "Horn o' plenty," the tech said absently and bent over the dirt.

It was hardly a cornucopia but for forensic purposes the residue was as big as a mountain and might reveal a wealth of information. "Scope it, Mel," Rhyme ordered. "Let's see what we've got."

The workhorse of tools in a forensic lab is the microscope and although there've been many refinements over the years the instrument isn't any different in theory from the tiny brass-plate microscope that Antonie van Leeuwenhoek invented in the Netherlands in the 1500s.

In addition to an ancient scanning electron microscope, which he rarely needed, Rhyme had two other microscopes in his homegrown laboratory. One was a compound Leitz Orthoplan, an older model but one he swore by. It was trinocular—two eyepieces for the operator and a camera tube in the middle.

The second—which Cooper was preparing to use now—was a stereo microscope, which the tech had used to examine the fibers from the first scene. These instruments have relatively low magnification and are used for examining three-dimensional objects like insects and plant materials.

The image popped onto the computer screen for Rhyme and the others to see.

First-year criminalistics students invariably click immediately on a microscope's highest power to examine evidence. But in reality the best magnification for forensic purposes is usually quite low. Cooper began at 4x and then went up to 30x.

"Ah, focus, focus," Rhyme called.

Cooper adjusted the high-ratio screw of the objective so that the image of the material came into perfect clarity.

"Okay, let's walk through it," Rhyme said.

The tech moved the stage, with imperceptible twists of the controls connected to the stage. As he did, hundreds of shapes scrolled past on the screen, some black, some red or green, some translucent. Rhyme felt, as he always did when looking through the eyepiece of a microscope, that he was a voyeur, examining a world that had no idea it was being spied upon.

And a world that could be very revealing.

"Hairs," Rhyme said, studying a long strand. "Animal." He could tell this by the number of scales.

"What kind?" Sachs asked.

"Dog, I'd say," Cooper offered. Rhyme concurred. The tech went on-line and a moment later was running the images through an NYPD database of animal hair.