1. Somebody put enough pressure on her carotid arteries, for long enough, to leave her all-but lifeless on the floor.
2. I was scoffing at the notion that some mystery assailant... left her for dead on the floor, all without a sound or a fight from Terri,
In your scenario, did Terri put up a fight, or not?
Why do you call it my scenario? What I or anyone else thinks about it is irrelevant. The truth is what it is.
Terri's blood tests showed lactic acidosis, an abnormal blood chemistry caused by violent exertion in the absence of oxygen. One may infer that she fought for a breath of air with everything she had. But it would have been hopeless with a man twice her size on her back, pinning her down.
John Doe arranges for his wife, Jane, to be killed while he is at work. It seems that she might divorce him and he is afraid of what her lawyer will unearth during the discovery phase of divorce proceedings. (What if that mobster learns that John was fooling around with his wife?) John is also the beneficiary of Jane's life insurance policy, and the money will help him settle some debts.
John expects to find Jane dead when he arrives home, but is surprised, when he walks through the slightly opened door, to find she is, unaccountably, still alive. (The "killer" had used a key, but left the door unlocked/open, when he departed, to make it seem that his John's wife had opened the door to an intruder.)
John Doe stays out of Janes' sight while he tries to find a solution. Should he call 911? Should he give Jane CPR? Should he leave Jane alone and hope she dies soon? (How long can he sit there and wait for her to die?) Should he make sure she dies?
What to do? What to do? Time passes while John sits on the sofa, where Jane cannot see him, and tries to piece together a story. He decides against killing her or giving her CPR because doing either of those things might cause someone to question how she had been treated before help (or the medical examiner) arrived.
John finally realizes that too much time has passed for him to say that he came home from work and found Jane on the floor.
So John makes up a story that he was in bed when he was awakened by the sound of his wife "collapsing."
That's the only story that will seem appropriate in the early morning hour when he finally contacts Jane's family... he was home, he was in bed, he heard his barely breathing wife collapse.