These "reasons that people murder" made me ponder from the psychology perspective (I am currently studying Psychology in my Master's) that perhaps with people that are willing to go to the extremes (as incomprehensible as that is), the universal needs also go way beyond normal?
One theory that is widely used to categorize these universal needs is the Self-Determination Theory (SDT). A key proposition of this theory is that human beings have deeply evolved psychological needs to be competent, autonomous, and related to others.
According to the SDT theory:
Autonomy refers to the need for doing things because we choose to do them, and enjoying that freedom of decision.
Competence refers to the need to feel that we have the ability to do what we wish to do, or the things that we choose, and be confident that we can carry them out.
Relatedness refers to the need for human connections that are secure, caring for others, and being respected.
This is just pure speculation on my part, and hugely MOO as I am not a clinical psychologist, but perhaps these people who see these extremely incomprehensible actions as a solution feel these kinds of needs in a very, very, very distorted way (something that is not understandable for the most of us).
This is in any way not meant to discount the actions, and it might not even be possible to ever rationally understand these very irrational, distorted minds. Just trying to somehow connect where these horrible reasons might stem from.