Human beings are inherently...?

This is definitely the scariest true story I have heard in a very, very long time.

Girls 'felt right' killing friend

The two 17-year-olds, who cannot be named, stuffed a chemical-soaked cloth into the mouth of Eliza Jane Davis, 15, and throttled her with wire after waking up on a sleepover and deciding neither would feel bad about killing someone. [...] The two teenagers, then aged 16, stayed in one room and decided to kill Davis the next day during a morning chat. The girl who carried out the strangling told police she watched calmly as the emotions on her friend's face shifted from anger to terror as she realized they intended to kill her.

Holy. Crap.