I don't think that the man is just a crippled psycho in disguise. Smart people can't avoid thinking logically, even if their acts seem irrational. There is always a subjacent current of logic... And here comes the third option
3. The women did something that was taken as a menace to his current ego/status and elicit a strong 'defensive' reaction.
The journalist can't be a menace for his wife or family (It seems they are publicly in an open relation). So probably is not sexual.
The man loves with passion other thing; His work. Maybe she did something that was seen as a menace against the other love of his life, his submarine. Maybe she poke around and tried to sneak/photograph/open/discover some parts of the engine with the purpose to earn some bucks selling the submarine secrets when returning to China. I'm speculating of course, but unless he was drunk or drugged (unprobable while driving a sub), or both where flirting for months by e-mail and he feels cheated, there should be a solid reason for she being 'punished' with death. This is not a random act IMAO.