toothbrush and for that matter shesariver I am not "trying to blame" a partner, just to understand, which I realise is pretty fuitile. I absolutely agree that this is inexplicable. That whatever the circumstances what this woman has done could never be justified. It's possible that the perpetrator can shed light on her motives, though I doubt she will come up with anything that most of us can see as a reasonable explanation. I accept the possibility that like Brevik she is absolutely sane, and that she acted alone, without influence of others, and is evil. Even evil people have motivations, even if they are not ones that we can understand.
I am not naive enough to think that women are not capable of horrendous crimes against others, and to do so independently of men. I also know that occasionally people (men and women) find themselves put in unbearable situations by others (including partners) that push them to do unthinkable things. Things that they might not actually have gone through with alone. I'm thinking of Rosemary West, who committed some crimes alone and some with her husband, though her offending only started after her relationship with Fred began.
I am also open to the possibility that there is an explanation (which yes, I do understand, is not the same as a justification) beyond this.