The Motivating Factors for a Serial Killer

When there is a co-conspirator, do you know who tends to come up with the idea first? Is it usually the woman? I would think the male. So even if it was, let's say, the male's idea to commit the crime, I think the females in these duos are the one planting the seeds and kind of watching them grow as it comes specifically to parasite. What tend to be the motivating factors for someone to commit parasite? Well, very often it's serious family discord. Or they're extremely antisocial and motivated by so greed and also not wanting their parents to obstruct what they want to do.