Okay. How bout this lol. Since there's no abduction or kidnapping charge, I have to toss that he filmed her murder.
How about she goes to his house, goes in his garage, or is in his driveway, he pulls up, doesn't see her, runs her over. She's badly injured, he panics, and he suffocates her.
LE finds evidence on the car - blood, tissue, etc, that supports that part of his story.
So how do they know he suffocated her - they can't just take his word for it. Well, what if they have a security system on the house that films the area of the garage or driveway or wherever this happened?
Evidence tampering could be that he took the car to a car wash maybe?
I think that accounts for the charges we have - and the ones we don't have (e.g. abduction/kidnapping) - except... armed criminal action.
We'd need to know two things - was the car impounded, and do they have a security system with cameras on their house. And we'd need to account for that armed criminal action - unless the weapon for that was, as cluciano mentioned, perhaps a pillow or plastic bag.
This is driving me out of my mind and I know my head is going to be going for hours when I go to bed.