The Prom Night Killer (S08E05)

In 1989, Jessi Toronjo attended a sleepover, convinced her stepbrother, Jeffrey Pelley, was at his senior prom. For the next 13 years, she was under the impression that another person was responsible for a horrific crime that occurred that weekend. However, she ultimately unearthed a shocking truth: the perpetrator was someone she had known all along.