"So he did it after the killing," Rhyme said. "It's probably an obscuring agent."
Diligent perps would sometimes use a powdery or granular material of some kind--sand, kitty litter or even flour--to spread on the ground after committing a crime. They'd then sweep or vacuum up the material, taking most of the trace particles with it.
"But why?" Rhyme mused.
Sachs stared at the body, stared at the cobblestone alley.
I'm him. . . .
Why would I sweep?
Perps often wipe fingerprints and take the obvious evidence with them but it's very rare when someone goes to the trouble of using an obscuring agent. She closed her eyes and, as hard as it was, pictured herself standing over the young man, who was struggling to keep the bar off his throat.
"Maybe he spilled something."
But Rhyme said, "Doesn't seem likely. He wouldn't be that careless."
She continued to think: I'm careful, sure. But why would I sweep?
I'm him. . . .
"Why?" Rhyme whispered.
"He--"
"Not he," the criminalist corrected. "You're him, Sachs. Remember. You."
"I'm a perfectionist. I want to get rid of as much evidence as possible."
"True, but what you gain by sweeping up," Rhyme said, "you lose by staying on the scene longer. I think there has to be another reason."
Going deeper, feeling herself lifting the bar, putting the rope in the man's hands, staring down at his struggling face, his bulging eyes. I put the clock next to his head. It's ticking, ticking. . . . I watch him die.
I leave no evidence, I sweep up . . .
"Think, Sachs. What's he up to?"
I'm him. . . .
Then she blurted, "I'm coming back, Rhyme."
"What?"
"I'm coming back to the scene. I mean, he's coming back. That's why he swept up. Because he absolutely didn't want to leave anything that'd give us a description of him: no fibers, hairs, shoe prints, dirt in his soles. He's not afraid we'll use it to track him to his hidey-hole--he's too good to be leaving trace like that. No, he's afraid we'll find something that'll help us recognize him when he comes back."
"Okay, that could be it. Maybe he's a voyeur, likes to watch people die, likes to watch cops at work. Or maybe he wants to see who's hunting for him . . . so he can start a hunt of his own."
Sachs felt a trickle of fear down her back. She looked around her. There was, as usual, a small crowd of gawkers standing across the street. Was the killer among them, watching her right now?
Then Rhyme added, "Or maybe he's already been back. He came by earlier this morning to see that the vic was really dead. Which means--"
"That he might've left some evidence somewhere else, outside the scene. On the sidewalk, the street."
"Exactly."
Sachs slipped under the tape out of the designated crime scene and looked over the street. Then the sidewalk in front of the building. There she found a half dozen shoe prints in the snow. She had no way of knowing if any of them were the Watchmaker's but several--made by wide, waffle-stomper boots--suggested that somebody, a man probably, had stood in the mouth of the alley for a few minutes, shifting weight from foot to foot. She looked around and decided there was no reason for anybody to be standing there--no pay phones, mailboxes or windows were nearby.
"Got some unusual boot prints here in the mouth of the alley, by the curb on Cedar Street," she told Rhyme. "Large." She searched this area too, digging into a snowbank. "Got something else."