Now that would be a big laugh to see him come up with that one. You don't "accidentally" strangle someone to death.
It would surprise me, but if this truly was a case of simple workplace violence, it is very unlikely that it started off as a strangling. But we also don't know for sure the method of strangulation yet.
Arguments can escalate quickly and it could be a scenario something like: him admonishing her about something, she finally getting tired of it and putting him in his place, him snapping and pushing or cornering her, she threatening his job "I'm reporting you," trying to leave and getting attacked, her yelling for help and/or fighting him off and him trying to shut her up in a fit of total and desperate rage.
There's just no way this was premeditated. He HAD to know about the security cameras and that the card swipes were recorded. This was a heat of the moment argument gone completely out of control, followed by a desperate attempt to conceal the crime.
It will be very interesting to see what motive the DA comes up with. They definitely have opportunity, but motive is still unclear.. at least to the public. If they can't come up with any evidence of a relationship (whether it existed or not), they will use what will stick. They don't want this guy back out on the streets.
The details will come out as the case heads for trial. Interesting case, and very tragic all around.