Thank Neuromancer and I take your point(s). It's just that TM seems to me to be as cunning as an outhouse rat, or am I flattering her too much?
Dunno Makara - I just see her as naive and gullible and a victim of a narcissistic seducer too. These guys can be ridiculously charismatic when they're on the hunt. I mean, she fell for "my marriage is over but I can't possibly leave her because of xx", "we don't sleep together any more" and all the rest of those lines that should ring warning bells, so it sounds like she was infatuated very quickly and all sense went out the window.
I suppose looking at it strategically, I think he only would have told her if he really needed to use her for some part of it, because otherwise she'd be too much of a loose canon to take the risk of involving her.
This may be coloured by my opinion that, while he may have been fantasising about murdering A (to solve all his problems) and maybe plotting to some degree, the actual murder took place in a fit of rage during a fight with A (while still pissed off after being yelled at on the phone by TM and furious at how little control he had over his life) that reached a point of no return and he took the chance to do it there and then. Maybe he'd already hit her, she tried to call the cops, he knew the last thing he needed right now was an assault charge, etc
I think if it had been totally pre-meditated it would have been neater. Maybe a fall while bush-walking or something.