Richie didn’t look convinced. I said, “You think I’m being hard on them? Society’s given them a raw deal, and I should have a little more empathy?”

“Not exactly. Just … if he’s got no control, then how’d he manage to hold back for so long?”

I said, “He didn’t. We’re missing something.”

“How d’you mean?”

“Like you said, this guy spent at least a few months, probably more, just watching the Spains, maybe occasionally sneaking into the house when they weren’t around. That wasn’t his amazing self-control in action: it was because that was all he needed to get his fix. And then, all of a sudden, he comes charging out of his comfort zone: jumps from binoculars straight to full-on close contact. That didn’t come out of nowhere. Something happened, in this last week or so; something big. We’ll need to find out what that was.”

In the interview room, our man knuckled his eyes, stared at his hands like he was looking for blood, or tears. “And I’ll tell you one more thing,” I said. “He feels very emotionally connected to the Spains.”

Richie stopped drawing. “You think? I was thinking it wasn’t personal. The way he kept his distance …”

“No. If he were a professional, he’d be home by now: he’d have clocked that he’s not under arrest, and he’d never even have got into our car. And he isn’t a sociopath who saw them as just random objects that looked like fun, either. The soft kill on the kids, the close-contact kill on the adults, wrecking Jenny’s face … He had feelings for them. He thinks he was close to them. More than likely the only actual interaction they ever had was when Jenny smiled at him in the queue at Tesco; but in his head, at least, there was a connection there.”

Richie breathed on the glass again and went back to his patterns, more slowly this time. “You’re taking it as a definite that he’s our man,” he said. “Yeah?”

I said, “It’s early days to call anything definite.” There was no way to tell him that the drumming in my ears had swelled so high, in the car with this man at my shoulder, I had almost been afraid I would have us off the road. The man permeated the air around him with wrongness, strong and repellent as naphtha, as if he had been soaked in it. “But if you’re asking for my personal opinion, then yes. Hell yes. This is our man.”

The guy raised his head as if he had heard me, and his eyes, rimmed with painful-looking swells of red, skidded around the room. For a second they rested on the one-way glass. Maybe he watched enough cop shows to know what it was; maybe the thing that had fluttered through my skull in the car moved both ways, shrilled like a bat at the back of his neck to warn him I was there. For the first time, his eyes focused, like they were staring straight into mine. He took a quick deep breath and set his jaw, ready.