The Murder of Adrianne Reynolds & Other Stories

The murder of Illinois teenager Adrianne Reynolds made national headlines after she was strangled and dismembered by two of her classmates, Sarah Anne Kolb and Cory Gregory in 2005. Sarah and Cory would take Adrienne's body to Sarah's grandparents' farm where they attempted to burn it to no avail. They would then recruit another friend to help dismember the body after which they would dump it in a historic site. The three then went and ate lunch at McDonald's to celebrate their crime. What would ever possess these teens to commit such a horrific crime?