Well, I don't think if there was SA that it happened in the trunk. Is anyone giving that serious consideration? Come on.
Iirc, JMOM said the location of the bite on EA led her to believe he was bitten while outside of the car. And his other injuries indicate a fight with someone.
So, a scenario? Christina is hit (by a car door, by a fist) and knocked out at EA's car, thrown in his trunk. He leaves garage, drives away. Maybe CM comes to, uses trunk release latch, or comes to and is able to attack EA when he stops wherever and opens the trunk. Fight ensues, she does not win. She is murdered, with or without SA. He drives back toward the Shops, maybe to leave CM near her car, then heads home, leaving lots of questions in his wake.
All roads relating to Christina's current situation lead back to EA, whether or not anyone else was involved. He has all the answers, whether or not anyone else was involved.
(By a car door - how casino man incapacitated a woman who walked with him out to parking lot, he smashed her with car door, threw her in the back seat, and drove away. By a fist - we've probably all seen a video of someone getting cold cocked, out like a light. And one minute would have been sufficient, let alone three.)
IMO, of course.