He knows where the key is, obviously. It's not under the doormat, but in, stuck through the clever little hole on the bottom. One doesn't just stealthily stake out a house without knowing these these things, of course. One also doesn't do so without finding out the basic schedule of their victim. For instance, she should be done with her shower soon, and with the boyfriend always hassling his detective partner on Tuesdays, she's all alone. The perfect time to make a move.

So, with the key he cleverly found, he opens the door without knocking, and as expected she cannot hear him because of the running water. He waits a bit, taking in what he's only seen from the outside through windows: the sickeningly inviting warmth of a living room right by the front door, and pineapples that are strangely strewn everywhere.

She comes out of the shower in only a bathrobe, wringing out her wet blonde curls, and he smiles slyly. It is so sweet how oblivious she is of his existence in the house as she waltzes around during her nightly routine. Approaching with his pistol in hand, he swings at her, and Juliet O'Hara blacks out.