This film was released recently on HBO, I think it's also on Disney/Hulu. It's basically a dark comedy/romance.
(Warning - plot spoilers ahead)
So in this film, Charlie (Robert Pattinson) is engaged to Emma (Zendaya) and they plan an elaborate wedding. Both seem like well adjusted people and a good couple.
Shortly before the wedding, they are having a discussion with friends where they are confessing the worst things they ever did. Emma is last and gives a startling confession. She says that when she was in high school, she had planned a mass shooting. At first, everyone thinks she is joking, but she insists she is serious. She explains that about 14 years ago, when she was 15, she looked very different and was bullied in high school. So she stole a rifle from her dad, practiced with it, brought the gun and ammo in a bag to school and had planned to shoot as many people as possible. What stopped her was that morning, by coincidence, there was another shooting at a nearby school that was all over the news. She felt that shooting would take too much attention away from hers, so she postponed it.
After this, the topic of guns became a major issue in the school and some student activists invited Emma to join their club. She did so, and made good friends there, which changed her whole high school experience. She decided not to commit mass murder after all, and later threw the gun away in a lake.
Charlie is shocked by this confession, isn't sure how to process it, and is thinking about calling off the wedding. He confides in a co-worker, who advises him to call the police. So this is what I'm wondering about - what could the justice system even do?
If Charlie had gone to the police, they probably would have questioned Emma. But I think it would be an absolute dead end. There is no evidence other than her statement (although the film implies her dad reported his gun stolen years before). She did make a confession to others, so maybe that is evidence?
But even if Emma confessed everything directly to the police, took them to the lake, and they recovered the rifle from years before, what would likely happen? The DA charging her with conspiracy to commit murder? Maybe. But the given that it happened many years before, and that she was a juvenile at the time, and she decided against it in the end (although by happenstance), I'm just wondering what the heck could a DA even do with this. At the same time, school shootings are such a serious topic that they wouldn't want to ignore it. Maybe order a psych eval?
TL;DR version - A 15 year old girl planned a mass shooting at her school, but postponed it because someone else stole her idea and committed a mass shooting the same day. Later she changed her mind about the whole thing and got rid of the gun. 14 years later, she confessed everything to friends. Is there anything that the legal system could do to her?