Apologies in advance for the long post.... I know there has been speculation about what may have set RC off down the deep end. We now know from the autopsy that the ME indicated she was
struck first before strangled.
Here's a possibility. Just think if you were Annie, and you're in an isolated room with a guy who is taller, bigger, stronger and heavier than you. You're having a debate about cage cleanliness, and this bigger person is clearly becoming more angry and intimidating and needing to prove his point as "Lord of the Lab" (term, courtesy of tv's JVM).
So what would you do? You'd turn around and....
leave.
I know it has been reported that Annie was feisty, but we also know she was also very smart. It probably became clear to her that this debate was getting her nowhere. No matter the angle she approached this issue, it was clear he was just NOT going to acquiesce or compromise on the issue.
I would bet that at that at some point she recognized this and turned around to leave and THIS was the action that set RC off. He could no longer press his case with her, and be right; it was interpreted by him as a sign of rejection towards him (his ideas, possible fixations, job status etc), and probably made him feel lower than low. So when she turned around to leave, this action blew his top off like hot lava in a volcano.
So then what did he do?? He lashed out and struck her. And
once he struck her, there was no turning back. After all, she could call the police, file a complaint, and then his job would probably be done for.
(He may have been unionized. In some unionized jobs, there typically has to be a series of mishaps before someone can be dismissed. However, striking another employee is one thing that cuts through all the red tape. From my experience as an employer, even an unionized employee can lose their job in an instant for striking a fellow employee.)
So then he was enraged, and seeing red, and all this was directed towards her. And then he couldn't let her go, because his livelihood--the only job he knew since high school--would be kaput.
If the strike didn't disable her, then she probably kept trying to get away. And so he kept strangling her until he killed her. In his crazed mind, there was no other choice.
Again, so sorry for the long post. All this to say that I'm betting Annie attempted to leave the escalating situation, and wondering if this was the slight (in RC's mind) that set him off.