RoseMontague said:
One person could probably grab her with one hand and stab her with another.
Yes, if you go back to discussing the dynamic of the attack in relation to the wounds found at the autopsy, I see it synthetically like this: Meredith was forced to suffer a certain number of acts of violence at the same time – which means: the attacker had to commit a series of actions, a number of which necessarily had to be done at the same time in some moments.
1. she was prevented from using both her arms both during the attack with the knife and during the sexual assault (attacker needs to engage one hand at least to block her arms)
2. she was forcedly prevented from screaming by covering her mouth (I don’t know if the attacker employed his/her right hand or left hand, but it is possible to infer it). She was prevented from screaming throughout a time of duration of violence, albeit she could scream at some point.
3. she was threatened with a knife (for which her hands show small cuts indicating a mild defensive response to a non mortal threat; attacker requires a hand to handle the knife)
4. she was stabbed with a knife twice, with movement that in both cases can be defined puncture, not slash, on the two different sides of her neck (attacker requires at least one hand in two separate moments)
5. she suffered a sexual violence while she was alive and she still had her trousers or not removed (attacker requires one hand for this)
6. she was immobilized in the room. There was no real struggle, she could not move from the beginning of the attack: this is obvious by the fact that almost all light objects are still in their place in the room.
7. she had the strap of her bra forced with hands and then cut with a knife.
Some of this points have obviously appear likely only if considered to happen at the same time, because of the necessity of the assailant to hold a weapon. If the attacker is using one hand to grab her mouth and one hand to assault her sexually, he as no hands left to hold the knife or to block her hands. If he holds the knife and rapes her with one hand, or uses the same hand to grab her arms, he can’t be safe she won’t scream, or won’t attempt a fight or an escape around the room. If he is threatening her with the knife, and at the same time attempts remove her trousers and rape her, the chances that while doing this he is able to block her hands - to the point of finding no biological matter on the tip of her nails – is quite reduced. Practically, in a lone-attacker scenario Meredith never screams (even if the grip on her mouth demonstrates her intention to scream), never attempts to fight and never moves, never attempts to defend herself from the blade with her hands, while the attacker manages to both rape her and constantly hold a knife.
I think that this dynamic – this system of shifts - appears unlikely at a first glance to the say the least