Your angle is a good one, except that this particular person knew what he/she was doing. One of that person's responses to me was, "It was time (for their parent) to die."
I understood that. I was answering your question "How do you explain...."; the quotes in my response were to suggest what you could say to such a person. Your angle is a good one, except that this particular person knew what he/she was doing. One of that person's responses to me was, "It was time (for their parent) to die."
If they understood from the get-go that what they were seeking was nothing less than cold-blooded murder, then mustering sufficient contrition to achieve atonement will be very difficult. But in that case, their heart wasn't hardened by their actions--it was pretty stony to begin with.
If they kinda sorta felt that it was wrong, but didn't think it was really murder, then you could focus on the fact that they'd been duped into thinking it was only kinda sorta wrong, and at least some of their sorta-loved-one's blood was on the hands of those who duped them.