Because, why wouldn't he? Everyone's life is valuable. Everyone is worthy. The murderer's lack of understanding of the victim's worth, his clouded vision, doesn't have to translate to the clouded vision of the judge. Two wrongs don't make a right.
Whatever way someone is, there are always reasons, so we should be forgiving.
Here a couple of excerpts from a couple of books I have:
But some people are basically evil. Some people are intrinsically bad.
Who told you that?
It is my own observation.
Then you cannot see straight. I have said it to you before: No one does anything evil, given his model of the world. Put another way, all are doing the best they can at any given moment.
All actions of everyone depend on the data at hand.
I have said before—consciousness is everything. Of what are you aware? What do you know?
But when people attack us, hurt us, damage us, even kill us for their own ends, is that not evil?
I have told you before: all attack is a call for help.
-'Conversations with God book 2', Neale Donald Walsch
No one truly desires to hurt another. Those who do it— including your own governments, by the way—do it out of a misplaced idea that it is the only way to get something they want.
Have you ever wondered how you might behave in someone else's shoes? If you have, you'll likely admit that this kind of thinking is usually critical of the person of the person you're thinking about. The truth is, you are the other person, and they are behaving exactly as you would if you were indeed in the exact same shoes--however inconsiderate, abusive, outrageous, or immoral their behavior is.'
'True, you are probably more thoughtful, fearless, loving, and honest than those who disappoint you. But you are also at a different point in your journey, maybe "more advanced," or maybe just more at ease for having chosen a less "challenging" path. We're all of "one," exhibiting different colors of the same light, and rather than passing judgment, it's best to remember that each of us is just doing the best we can.'
-'Choose Them Wisely: Thoughts Become Things!', Mike Dooley
Then there is there is my RetroSpring answer from a few years ago to the question, "Is hatred ever truly justified?" (You never simply "devalue someone's life" because they're evil--your default position of valuing their life becomes occluded by hatred): https://philosophy.inhahe.com/2017/02/05/is-hatred-ever-truly-justified/
