help me

need help find a show? not sure if it's a documentary or if its just a show but here's what ik abt it ° the main character was a blonde girl and she had a weird last name and she's the one that got murdered ° she was killed at a party ° they are all in high school ° I can't remember exactly but I think everyone thought that this girl who was carrying a pocket knife killed her when in reality it was the boyfriend but again not too sure about that.

and no it's not a good girl's guide to murder, I think it's a documentary yeah because you could see actual footage when they went to the house of the girl that had the pocket knife