When MOM gets up his first questions should be: were you present at this event to see it ongoing? If not, are you able from the file to discern what Z was thinking while getting pummelled?
The threats are out there. The ME, EMT, police have all heard them. Police probably used to it. ME and EMT probably not so much. This has to have had an impact on testimony. The truth will have to be coaxed out by the defense.