I've seen the results of evil actions very clearly and it's awful. I can't imagine how prison warders and policemen cope with having to handle that sort of thing every day.
I've four times had a sensation of pure evil. One was completely inexplicable. I would like to dismiss it, but that seems like a denial of my own experience and a bad thing to do. But it is annoying that I can't explain it rationally!
The 2nd was a situation where I had to sleep in a certain room, it was the only one available. I and everyone else found the room really unnerving and there was a sense of malice. I dunno if it was the proportions of the room or the dim daylight or something.
The third time was closely attached to a rather lovely woman, but not her, herself. Like an invisible cloak around her. I can't explain it, it sounds stupid, but that's the closest I can get.
Did find out later something which makes me wonder if my intuition there was rather chillingly accurate, can't put it here, it would out her or me.
There's someone who's a convicted paedophile at the end of the road here but strangely, I don't get the same sense. This particular man is odd, but not evil (and yes, I'm well aware that most people would hang him or burn him alive given his conviction).
I have had the sense of evil from some inmates of a youth prison in the psychiatric wing though. I don't think they should ever be let out, though that's not really a legal possibility. They are so very, very clearly damaged and damaging beyond repair. Twisted childhoods and they have become twisted, pitiable but extremely dangerous teens and adults.