And even if he had regular bullets, the ricochet off metal and the stone and brick walls could kill or wound as easily as a direct shot.

She peered up the tunnel again and saw no movement.

‘Clear, Rhyme.’

‘Good. So. Let’s get going.’ He’d turned impatient.

Sachs already was. Wanted to get out of here.

‘Start with the vic.’

She’s more than a victim, Rhyme, Sachs thought. She has a name. Chloe Moore. She was a twenty six year old sale clerk in a boutique that sold clothing with loose strands escaping the stitching. She was working for near minimum wage because she was intoxicated on New York. On acting. On being twenty six. And God bless her for it.

And she didn’t deserve to die. Much less like this.

Sachs slipped rubber bands on her booties, the balls of the feet, to differentiate her footfalls from those of the perp and the first responders – whose footgear she would photograph later as control samples.

She walked closer to the body. Chloe lay on her back, her blouse tugged up to below the breasts. Sachs noted that even in death her round, pretty face was distorted with an asymmetrical grimace, muscles taut. It was evidence of the obvious pain she’d experienced, pain tapering to death. She’d frothed at the mouth. And vomited copiously. The smell was vile. Sachs mentally moved past it.

Chloe’s hands, under her body, were secured in cheap handcuffs. With a universal key Sachs removed these. The victim’s ankles were duct taped. With surgical scissors Sachs clipped the tape and bagged the gray, dusty strips. She scraped beneath the young woman’s deep purple fingernails, noting fibers and bits of off white flecks. Perhaps she’d fought him and if so bits of valuable trace, even skin, might be present; if her killer was in the CODIS DNA database, they might have his identity in hours.

Rhyme said, ‘I want to see the tattoo, Sachs.’

Sachs noted a small blue tattoo on Chloe’s neck, right and near the shoulder, but that had been done long ago. Besides, it was easy to see which one the killer had done. She knelt down and trained her eyes, and the camera, on Chloe’s abdomen.

‘There it is, Rhyme.’

The criminalist whispered, ‘His message. Well, part  of his message. What do you think it means?’

But given the sparse letters, Sachs realized, his question had to be rhetorical.

The two words were about six inches long and ran horizontally one inch above the woman’s navel.

Although he’d presumably used poison, not ink, the inflamed wound, swollen and scarring, was easy enough to read.

‘All right,’ Rhyme said, ‘“the second.” And the border, the scalloped lines. Wonder what those are about?’

Sachs commented, ‘They’re not as swollen as the letters. Maybe there was no poison in them. They look like wounds, not tattoos. And, Rhyme, look at the characters.’

‘How well done they are?’

‘Exactly. Calligraphy. He’s good. He knows what he’s doing.’

‘And another observation. It must’ve taken some time to do. He could’ve written them crudely. Or just injected her with the poison. Or shot her for that matter. What’s his game?’

Sachs had a thought. ‘And if it took awhile, that meant she was in pain for a long time.’

‘Well, yes, you can see the pain reaction but I have a feeling that was later. She couldn’t have been conscious while he was writing his message. Even if she wasn’t trying to get away, the involuntary movement would’ve ruined his handiwork. No, he subdued her somehow. Any trauma to the head?’

She examined the woman’s scalp carefully and looked under her blouse, front and back. ‘No. And I don’t see any signs of Taser barbs. No stun gun welts … Ah but, Rhyme, see that?’ She pointed out a tiny red dot on her neck.

‘Injection site?’

‘I think so. I’m guessing sedative, not poison. There’s no sign of any swelling or other irritation that toxin would cause.’

‘The blood work will tell us.’

Sachs took pictures of the wound and then bent down and swabbed the area carefully, lifting trace. Then the rest of her body too and the ground around her. It was likely that a perp this diligent would have worn gloves – it certainly appeared that way. Yet valuable evidence from even a gloved and gowned perp could still easily be transferred to the victim or crime scene.

Edmond Locard, the French criminalist who lived a century before, formulated the Exchange Principle: that every time a crime occurs there is a transfer of evidence between criminal and scene, or criminal and victim. That evidence (which he referred to as ‘dust’) might be very, very difficult to detect and collect but it exists, for the diligent and innovative forensic scientist.

‘There’s something odd, Rhyme.’

‘Odd?’ A splinter of disdain for the artless word. ‘Go ahead, Sachs.’

‘I’m using only one of the first responders’ spotlights – the other’s pointed up the tunnel. But there’re two shadows on the ground.’ She looked up and walked in a slow circle to get a clear view. ‘Ah, there’s another light near the ceiling, between those two pipes. It looks like a flashlight.’

‘Not left by the first responders?’

‘What cop or medic is going to give up his Maglite?’

The big black tubed flashlights that all cops and firemen carried around were invaluable – great sources of illumination and they doubled as bone breaking weapons in a clutch.

But she noted it wasn’t one of those expensive models. This was cheap, plastic.

‘It’s taped to the pipe. Duct tape. Why would he leave a light here, Rhyme?’

‘That explains it.’

‘What?’ she asked.

‘How the store manager found the body. The flashlight. Our perp wanted to make sure we found the message from our sponsor.’

The words seemed a little flippant to Sachs but she’d always suspected that much of Rhyme’s gruff façade and sardonic delivery were defense mechanisms. Still, she wondered if he raised the barricade of protection higher than he needed to.

She preferred to leave her heart unguarded.

‘I’ll collect it last,’ Sachs told him. ‘Every bit of light helps.’

She then walked the grid, which was Rhyme’s phrase for searching a crime scene. The grid pattern was the most comprehensive approach in looking for evidence and assessing what had occurred. This technique involved walking slowly across the scene, then pivoting and moving one step to the right or left and returning to the far side. You did this over and over until you’d covered the entire space. Then you turned 90 degrees and covered the same ground again, perpendicular. Like mowing a lawn twice.

And with each step you paused to look up and down and side to side.

You smelled the scene too, though in this case Sachs couldn’t detect more than Chloe’s vomit. No methane or feces, which surprised her, considering that one of the pipes here was connected to the city’s sewage system.

The search didn’t reveal much. Whatever implements the perp had brought with him he’d taken – aside from the flashlight, cuffs and strips of duct tape. She did make one find, a small ball of crumpled paper, slightly yellowed.

‘What’s that, Sachs? I can’t see very clearly.’

She explained.

‘Leave it as is; we’ll open it back here. Might have trace inside. Wonder if it’s from her.’

Her. The Vic.

Chloe Moore.

‘Or maybe from the perp, Rhyme,’ Sachs added. ‘I found what looked like fibers of newsprint or paper under her nails.’

‘Ah, that could be good. Did they fight? Did she grab something of his? Or did he  want something she had and rip it from her fingers – while she struggled to hold on to it? Questions, questions, questions.’

Using additional adhesive rollers and a small handheld vacuum, Sachs continued the search. Once these samples had been bagged and tagged she used a separate vacuum and a new roller to collect trace from places as far away as possible from where Chloe lay and where the unsub had walked. These were control samples – natural trace from this area. If analysis back at the lab revealed, for example, a clay rich earth near one of the unsub’s footprints, which didn’t match any control specimens, they could conclude that he possibly lived or worked in or had some other connection to a locale loaded with clay. A small step toward finding the perp … but a step nonetheless.