‘He cleared the house, in case the assailant was still inside, which he wasn’t. When McCann was sure the guy was gone, he wiped the place down to get rid of his old fingerprints – honest to God, Conway, I’m going to need you to take off that superior disapproving face. I can’t concentrate while I have to look at that.’

There’s no expression on me at all; Breslin just wants me in the wrong. ‘If you don’t like my face,’ I say, ‘you can look at Moran. Or shut your eyes, for all I care.’

Breslin sighs, shakes his head and makes a big deal of turning his shoulder to me and focusing all his attention on Steve. ‘So McCann wiped for prints. He had a look around Aislinn’s bedroom to see if she’d kept any of his notes, which she hadn’t – at least, not in the obvious places. He considered sticking around in case the assailant came back, but he decided that was unlikely enough that it wasn’t worth the risk.’

Steve says, all puzzled furrowed brow, ‘Why’d he turn off the cooker? That’s been bothering me from the start.’

‘So that any evidence wouldn’t be destroyed—’ I snort. ‘Fingerprints aren’t everything, Conway. McCann knew the killer could have left behind DNA, hairs, fibres, valuable stuff; he wasn’t about to ruin that. And he didn’t want the place to catch on fire and burn Aislinn to death, if by some tiny chance he was wrong and she was still alive. And . . .’ Breslin smiles a little sad smile. ‘He didn’t say this to me, because Mac doesn’t like looking like a sap any more than you or I do, but I’m pretty sure he also couldn’t stand the idea of Aislinn’s body being burned. He was fond of her, you know.’

‘Aah,’ I say. I half expect Steve to move, signalling me to dial it back, but he doesn’t. Steve’s gone past wanting to be buddies with Breslin.

‘Conway. Just stop. I know you hate this squad and everyone in it, but think like a fucking detective for a second, instead of a teenage reject who’s finally got one up on the popular girls. If Mac had killed Aislinn, why would he turn off that cooker? He would have turned it up to full and hoped the place burned to the ground.’

I say, ‘What’d he do next?’

Breslin sighs through gritted teeth. ‘He went out the back door, locked it behind him and went home. Don’t bother checking the CCTV; you won’t find him. Not Saturday night, not any night. It’s easy enough to find out where the cameras are and plan your route around them. If it came to a divorce, Mac wasn’t about to give his wife anything a private dick could turn up to use against him.’