I wonder if the person who did this stabbed the dog to death so that it wouldn't bark and then took the dog away and dumped the carcass. Then, he went in through the door to the little girls room, grabbed her and either held his hand over her mouth or gagged her with something. Then, he took her out through the door since he was sure that no one had heard anything and gotten up. He then would have taken her to an area outside or possibly to a residence nearby where he could spend time with her, molesting her. He was afraid to come back through the door since he was getting spooked in that he'd had her out for a while. So, he breaks the window and just reaches her in through the window, thus giving her cuts all over her body, causing her to bleed. If he was careful enough, he could do it without himself getting cut or perhaps he had his hands and arms covered. If she was taken out through the window, LE would find a trail of her blood to the molestation site. I think that he went in and out through the door, carrying her. He couldn't risk his blood being at the site.
Such a terrifying scenario!