The actual facts are grewsome and perverted. You can read the full story in the Idaho Statemens archives using google. The girl was violently penetraded and abused. In Idaho, young age in a violent crime,is considered but can be overridden by the prosecuting attorneys.
I read the link, that’s how I was able to do the summary.
From your original post, I couldn’t tell if the incident had happened at school or off campus, which is why I looked. The dumping the vicim also seemed a relevant factor.
Still missing details include whether the parents of the perp were at home or not, and whether or not they condoned the party.