WARNING I'm going to be graphic..
We know their clothing was removed either by them or by the killer and to me that in itself is sexual assault. A child being asked to undress or being undressed is SA. Touching a child is SA.. he didn't have to (sorry to be graphic) insert anything or make them do anything to him or even him do anything that would leave his seman at the scene for it to be SA. If he took their clothing off and in any way touched them, THAT IS SA!
Defense can word salad it up because there is no evidence of it on their bodies (assuming no evidence of insertion of anything by leaving evidence of tissue damage, bruising, and/ or semen) does not mean that was not his motive and it doesn't mean that what he did do was not SA.