Commander Penn spoke. The reason we think he has been using this exit is we’ve discovered it has been tampered with. A folded strip of aluminum foil has been wedged between the door and its frame so someone could access the exit from above ground.

‘It’s also the closest exit to the pharmacy,’ Commander Penn continued. It’s remote, back here behind this building, basically in an alleyway between Dumpsters. Gault could go in and out whenever he pleased, and it’s unlikely anyone would see him, even in broad daylight.’

‘And there’s another thing,’ Lucy said. ‘At Cooper Square there’s a famous music store. The Carl Fischer Music Store.’

‘Right,’ Commander Penn said. ‘Someone who works there recalls Jayne. Now and then she wandered in and browsed. This would have been during December.’

‘Did anyone talk to her?’ I asked, and the image made me sad.

‘All they recalled was that she was interested in jazz sheet music. My point is, we don’t know what Gault’s connections to this area are. But they could be more involved than we think.’

‘What we’ve done,’ Lucy said, ‘is take away this emergency exit. The police have bolted it shut, and boom.’

She hit more keys. The symbol was no longer lit up and a message next to it said Disabled.

‘It seems that might be a good location to catch him,’ I said. ‘Why don’t we want him there behind the Cooper Union Building?’

‘Again,’ the commander said, ‘it’s too close to a crowded area, and should Gault duck back into the tunnel, he would be very deep inside it. Literally, in the bowels of the Bowery. A pursuit would be terribly dangerous and we might not catch him. My guess is he knows his way around down there even better than we do.’

‘All right,’ I said. ‘Then what happens?’

‘What happens is, since he can’t use his favorite emergency exit, he has two choices. He can pick another exit that’s farther north along the tracks. Or he can continue walking through the tunnels and surface at the Second Avenue platform.’

‘We don’t think he’ll pick another emergency exit,’ Commander Penn said. ‘It would place him above ground too long. And with a parade in progress, he’s going to know there will be a lot of cops out. So our theory is he will stay in the tunnels for as long as he can.’

‘Right,’ Lucy said. ‘It’s perfect. He knows the station has been temporarily closed. No one’s going to see him when he comes up from the tracks. And then he’s right there at the pharmacy - practically next door to it. He gets his money and goes back the same way he came.’

‘Maybe he will,’ I said. ‘And maybe he won’t.’