Imagine living with an abusive partner, or some kind of full-on modern slavery situation. If you can’t just flee (e.g. because it’s likely that they’ll come for you and abduct and/or kill you or your family), killing them might be the sensible course of action and needs planning, because if you were likely to win a head-on fight against the abuser(s) you probably wouldn’t be in that situation in the first place. Many jurisdictions will be relatively lenient in these situations, but you often still get a prison sentence.

And is it really that hard to imagine that your partner starts going Luigi? Harder than standard murder for immediate personal gain?