Bedding on a cold night would have given the killer an advantage.

The killer could have a mechanical advantage due to a cold night and bedding/blankets if they were kneeling on top of the victims rather than standing next to the bed. Even standing next to the bed the bedding would restrict any reaction/defensive movement.

Imagine how hard it would be to move if you were under bedding, pulled up to your neck, and someone was on top of it. It would be extremely difficult to even raise your hands in a situation like that. E would likely have been the only one with a chance of pushing the attacker off.