See I think it goes more like this;
They seem to be friends, buddies, no sexual tension.
I don't think this was her first time going to his room.
Just a feeling I get from the video and his body language.
I don't think violence or sex was his motive.
Just money.
She has told him about the laptop money.
He knows she has won some money playing cards.
She has been fighting with Dad, goes up to his room, they hang out.
There are five cigerrettes which would indicate she was there for a little while. She might have taken her own jeans off to sleep if Mr. Charming told her she could have the bed. You know what a good guy he is.
She wakes up to find him looking for her cash and credit cards. There is a confrontation, he hits her, knows in that moment he is F'ed. He has just assaulted a woman and with his past he knows this is huge problem, and he knows this is a daughter of privilege, he goes ballastic, blind rage, beats her to death.
To the sociopath that was his money, how dare she interfere with his plans, and now look at the mess she has made. I think that is the hatred you see in the beating, not sexual violence.
If they ruled out sexual assault they look for more than seminal fluid. There are abrasions and minor tears that happen in the process. And not to be graphic, but her pants were off, he clearly was able to overpower her, why isn't there signs of sexual assault?
She has her shirt and panties and pad on, sounds like sleeping clothes to me. But we will probably never know.