Sooner or later, he'll come back here. As I've pinched his latch key, he'll try the one in the handbag. When that doesn't fit, he'll realize his mistake, put two and two together, and look under the stair carpet.

If he doesn't do that, all of this is pure guess work. We can't prove a thing.

That's perfectly true. But once he opens that door, we shall know everything.