Some people are just bad seed.
Yes evil walks amongst us. One in ten people have anti-social or psychopathic tendencies. They are not crazy that’s a coping mechanism for people to self sooth themselves. There are evil people who are perfectly in charge of their mental capacity they just completely lack connection to society. One of my favorite Netflix shows is “The Method” it’s Russian but subtitled for those who don’t speak Russian. It’s like criminal minds but better.