They're still people. People who I'd be good with giving the death penalty, but still people. There's no need to de-humanize them - like only animals could do something terrible, not people. People are often the worst - way worse than animals - and have shown throughout history to be capable committing all kinds of atrocities.
I'm not sure if I've called anyone an animal before. Doing so takes them out of "our" group, and lumps them in with all the animals that can't control their worst/basest instincts. I believe that all people - as a species - are not above all that, or better than that, and most of them are only one or two bad turns/tragedies (or a chemical imbalance) from becoming that same thing. We're them, and they're us. Criminals and maniacs are the worst of us, but they're not different from us.