Every woman fears being murdered, but most don't suspect their demise to be in the hands of their best friend. But strangely enough, it happens more than you think. Buddies fight, drift apart, or even let men get between them. And then when one snaps, it can have deadly consequences. From teenagers who stabbed their pal simply because they "disliked" her to a woman who poisoned her bestie with cyanide, these true crime female killers are guilty of not only being terrible friends, but also vicious murderers.