C.M. Frankie

Julie Williams, Lollie Winans, Paul Fugate and others are among those who have been killed in national parks and whose cases have yet to be solved.

Ken Rex McElroy, a bully who menaced the farming community of Skidmore, Missouri for years, was shot and killed on July 10, 1981 outside a local bar. Witnessing the murder were McElroy's wife and dozens of local residents. Yet the gunman has never been identified.

Aiyana Gauvin, Adrian Jones and Roman Barreras are some of the high-profile cases from the past few years of children who were abused and ultimately killed by their parents. We speak with experts about why some parents unleash such extreme violence on their children.