Hi Andrea,
I am so sorry about David and I know the torture you are going through. We lost our son Adam to this in 2005, he was 12. I remember that if the kids have been doing this more than once, the coroner can find old bruising in the neck area and petechiae which is like a rash but it is broken blood vessels under the skin. This proves that the victim has been doing this for a while. I know there is a video out there of a coroner that found this research on how to investigate this. I know our coroner was just too busy to be bothered in investigating the cause and just left it inconclusive.

I hope this helps and I hope that you find peace. Sometimes the world just seems so upside down.