Didn't mean to teach granny to suck eggs, so sorry Hula. It's just that it's not the infidelity excuse that will save you from a murder rap, but whether or not it was premeditated.
I think in this case, they were leaning heavily on the fact he was on anti-depressants. I don't know which drugs they were, but there has been some evidence of people taking anti-depressants who have experienced significant personality changes and even psychosis. That wasn't proven in this case, but I would guess the jury weighed that possibility more heavily than the steps he took to prepare before the killing.
I'm also not suggesting that there wasn't institutionalised sexism at play in the decision. Jurors are likely to hold the same kind of prejudices as the general public.
I wish I'd kept it as it was only a paper copy, but I think it was around 1996, Channel Four TV did a piece of research about the use of please of manslaughter on grounds of diminished responsibility in the case of people killing their partners. If anyone can find it, you will be my mate forever.
Their study found that when a woman killed her partner, courts generally only accepted a plea of manslaughter due to diminished responsibility where she had a previous diagnosis of a mental illness. In cases where men killed their partners, they more often accepted the same plea without prior evidence of mental ill health. They were willing to be swayed by a professional testifying that they believed the defendant to be suffering from "extreme stress" or "reactive depression" or similar if he was a man than if she was a woman.
I don't have any recent figures for convictions to know if this still holds true. Anybody got them?