I don't recall what season it is, but two kids are in two different episode. They are a brother/sister pair. The brother is older than the sister. In the first episode, the brother kills a girl in high school with the help of his sister by setting up some sort of rig on the high school showers. I remember half way through out the episode, while in trial, the younger sister admits to committing the murder to save her brother. I also believe these two returned in a later episode. Anyone able to help me out?