They are people.
Calling them monsters and dehumanizing them separates "them" from "us" and prevents us feom trying to understand how a real person, with intellect, feelings, a family, a social life etc. can get to the point where they do such things. If we don't collectively at least try and understand it, we have zero chance of preventing it from happening again.
That being said, I'm not at all making excuses for their actions, which I find seriously violent, disgusting and worrying.