I was reading about a murder case last night involving three best friends - females all aged 16. Two of them decided that they "just didn't like" the other anymore and proceeded to lure her out one night to the middle of nowhere, stab her ~50 times and slit her throat to near decapitation. They then dumped her body somewhere, covered it with leaves/sticks and continued on with their lives as if nothing had happened.
They didn't get caught until over half a year later, but during that time they acted completely normal, even continuing to go round their murdered 'best' friend's house to console her parents. It was so weird reading through their Twitters which just looked like your average young teen's accounts, with tweets moaning about homework, arguments with parents, etc. All this despite knowing what they had done.
Blew my mind that young people are capable of these things, and with the sort of shocking stuff I see on social media these days I'm really surprised it's not more common. Kids are losing it.