What's with the whole nylon stocking thing?

After arriving home after the attack, Milland manipulates the crime scene with an eye to incriminating Kelly. He finds "Swann's" key, places the letter from Cummings in Swann's pocket, then finds and burns Swann's garrote/scarf, replaces it outside with one of Kelly's stockings, then purposely hides the other nylon under the desk blotter (which he later intentionally uncovers with the tea tray). Now, I can see why he got rid of the scarf since it was pre-knotted garrote-style and might indicate premediation. Also, since she admitted it was her stocking and was kept in her sewing basket, it seems unlikely that Swann would have had the time and foresight to find a murder weapon before running back behind the curtain. But why would she have hidden the second stocking under the blotter rather returning it to the basket? And what suspicions did Milland hope to raise by replacing one stocking outside and the other under the blotter? I suppose (tho' I don't remember it being raised by the police) that she could have used the stocking on herself to simulate bruises from the strangling, but why would she have taken out two stockings, and why hide the second?