If I was the prosecution I would want to keep all mention of Satanism, Ritual, Occult, Horrorcore music etc, OFF THE TABLE, the prosecution does not want any of that to come in to play as they want the jury to focus on the 4 victims and how they were gruesomely murdered by a person they let in to their home and trusted.
The defense on the other hand, at least if I am the defense, needs to introduce all sorts of crazy ideas, the music, the scene, the community, satanism, the occult etc, these are the smoke and mirrors that will lead to a hung jury or possibly acquittal. Like I said before the defense needs to turn this in to a witch hunt against violent music and its culture and community. Like it or not, and I personally do not, that is precisely what I would do to represent my client and give him his best chance. As distasteful as it may seem I would also not shy away, as defense counsel, from putting the parents on trial and questioning their decision to allow their children to enter in to this whole house of horrors community to begin with. Forget about Sam, the victims and focus on the music the scene and the community and its culture. Whatever it takes.
