Okay. Itachi must have either done it during the day, or in the evening. Sasuke came home late in the evening, and they were already dead. (as for those who'd mention that he came home during the night because of the full moon that had already risen in the sky, guys, have you never noticed a full moon high in the sky even during the day?) Killing so many people, ninja at that (which means that they'd struggle, a lot) means that there's bound to be some noise. A lot of noise. After all, there was some damage to the streets and buildings in the Uchiha part of Konoha. Why no one ever heard or noticed anything? Konoha is a village full with ninja, who are bound to be constantly on their guard. It seems so improbable they won't hear sounds of a battle or a struggle, especially if so many people were slaughtered.