I'm honestly grossed out by how many of you have 0 compassion towards criminals and consider them in a 100% black and white way. No matter how you twist your words or beliefs, criminals of all severities have human attributes and are as complex as us. Because of this there are rarely criminals who do their crime for no literal reason or just for fun, there's usually an underlying problem or motive, and deciding whether this motive is deserving a death penalty isn't always easy.
By assuming that criminals have no humanity and no background motives, that have to be taken into account, you are thinking in a very lazy, immature way and are also being 'ableist' by ignoring the possibility of a mental illness and the possibility of this mental illness being treatable. Instead you choose to look at criminals as an entirely different form of human beings and justify lack of empathy and rights towards them by it.
I want to expand on this as I feel it is directly linked to the idea of the death penalty. One of the problems with assuming murderers and other violent criminals are all bad, evil, not human etc etc is... that it's not true. We like to think someone like the one described in the OP is some strange twisted being who isn't human, isn't *like us*. It's scary to find out how utterly normal and mundane these mass-murderers were to people around them. It's confronting to realise that someone "evil" really can look and act and *be* just like any normal non-murdering human being.. until they start murdering.
The most common thing said about serial murderers and rapists by people who knew them is "but he/she was so normal I just can't believe it." Often it's "but he/she was so nice!" with a list of good deeds added. Statements like this come up in so many cases that it is very unusual to hear of a case where no witness makes such a statement. But regardless of who knew what and when, there is always this accusation (unspoken or otherwise) : how could they not have known? Because it is so very clear to everyone now, why wasn't it always clear?
There's a lot going on psychologically that explains why this happens, why people will go to such lengths - unconsciously - to use hindsight to paint that bad guy as utterly evil. But basically it boils down to : they are not like me. I am good, they are bad. I would never do ____ and they did. I had no idea they were capable of such a thing, they tricked me. I would have known otherwise. They are not just bad, they are evil. They are nothing like me. They aren't even human.
This mentality, this idea that we should be able to KNOW how bad a particular person is - even before they do anything to merit such a label - is dangerous. And faulty logic. But worse : it actively contributes to the suffering of the victims, and future victims of other crimes. When the attacker doesn't look evil, or "seem the type" then in general there's more trauma added to the victim/s in order to try and be heard and believed. People who have never knowingly talked to a rapist, a child abuser, or even a murderer tend to assume that those people just aren't around them. So they are more likely to dismiss any claims made against someone they know, just as countless other victims or witnesses have over the years..
The man who (allegedly) killed those people in Japan because he wanted to "help" them is a(n alleged) murderer. But he's just a man. Ignoring this reality doesn't make you (speaking generally) as bad as he is. But it sure doesn't help anyone either. He's just a man. Not a monster. Not a a demon*. Not evil. He broke the law, committed an absolutely reprehensible act by most anyone's standards, morals, whatever term you prefer. But he was once a baby, a child, a teen, and did all kinds of things that every human being does. Does that mean it's okay that he murdered those defenseless people? Of ****ing course not. But all the hyperbole does is isolate this man from his humanity, which may be of comfort to some but sure as heck does nothing to help understand the events in this situation. Or help us try and prevent such a thing happening again.
By painting people like this as evil, not human... you're only fooling yourself (again, speaking generally). Which isn't especially helpful when trying to prevent child abuse, rape, and sexual assault crimes. Statistically speaking : we all know people who have committed those crimes. They just hide it well.
* I'm not religious and my comment is not intended to counter nor reference any particular religious belief. The language I've used is meant to be applied in a secular fashion as is normal in society today, not to refer to anything biblical.