All LB:
Demon possession is not what you might think it is. We're not talking The Exorcist, Linda Blair type demon possession here, with green vomit etc. It can be hidden away so deep you would never know. Then something triggers them and their vile behavior comes out! Their thoughts are so corrupted due to not keeping their minds in control and honed to the word of God. Because of this, the devil can fool them and does fool them to the point they can't see right from wrong anymore. That's how they can justify killing or hurting babies, etc.
I knew someone for four years and didn't even know that there were times they'd be possessed. All of a sudden, their character would change. I mean the words they'd use were different, their vocabulary, even their voice would change slightly. I noticed 3 different characters in this one guy using 3 different types of speaking - one was the amiable guy that everyone loved, the other was the 'political' guy using very 'political' type language and very deceptive, the third was the very hostile/mean/angry guy. This is influence from evil spirits that makes people change that way where even their voice is different.