A commercial substance that was toxic, like those used in industrial processes and easily purchased on the open market, might be traced to a manufacturer and onward to a buyer. Some even had chemical tags that might lead investigators to receipts with the perp’s name on them. But that wasn’t going to happen if he dug his weapon out of the ground.

Impossible to narrow down beyond regions of the country. And presumably, the month being November, he’d picked the plant long ago. Or might even have grown it in a hothouse in his basement.

Equally troubling was the fact that he’d somehow reduced it to create a particularly virulent form of the toxin.

Ron Pulaski happened to be standing beside the whiteboard. Rhyme said to him, ‘Add that to the list in your concise handwriting, rookie, which the Sisters of the Skeptical Heart Church would be exceedingly proud of.’

Rhyme’s mood had improved considerably now that there were challenges to confront, mysteries to unravel … and they had some evidence to work with.

Sachs continued, ‘Now, there were no friction ridges.’

Rhyme hadn’t expected fingerprints. No, the perp was too smart for that.

‘As far as hairs – I found some from rats and some from Chloe but no others, so I’m guessing headgear beyond the stocking cap.’

Close-fitting hats tended to dislodge hair more than keep it from falling out, especially wool or nylon, since the wearer would tend to scratch or rub itches. Rhyme guessed the perp had known this and taken other, more careful precautions to keep his fiber and DNA evidence to himself.

She continued, ‘The prelim for sexual assault was negative – though the ME might find something else. But genitals and secondary sexual locations don’t seem to have been touched. Aside from her abdomen’ – she nodded at the photographs – ‘she was fully clothed. But when I wanded her with the ALS, I found something interesting: dozens of places where he touched her skin, stroked it. More than just to pull it taut to do the tattoo. And she had a small tat on her neck. A flower.’ Sachs displayed the picture on Rhyme’s high-def monitor. ‘He rubbed that a few times, the wand showed.’

‘But not sexual touching?’ Sellitto muttered.

‘Not traditionally sexual,’ Sachs pointed out. ‘He may have a fetish or paraphilia. My impression was that he was fascinated with her skin. He wanted to touch it. Or was driven to maybe.’

Rhyme said, ‘Driven? That’s getting a little fishy for me, Sachs. A little soft. Noted but let’s move on.’

They began on the trace, analyzing substances that Sachs had found near the body and comparing them with control samples from the tunnel, trying to isolate those that were unique to the unsub.

Cooper kept the GC/MS humming.

‘Okay, clustered together we have nitric oxide, ozone, iron, manganese, nickel, silver, beryllium, chlorinated hydrocarbon, acetylene.’

Rhyme nodded. ‘Those were near the body?’