My brain just keeps going back to the fact how could SS w all his martial arts training not have done something ...thrashed DW or sent him a judo kick .....texted help or said help in his messages or give any indication something amiss--SS must have seriously believed if he carried out all DW requests he would have saved his family. The entire thing is so unconscionable to me. That is why in my mind I HAVE BELIEVE there was someone else in the house with DW.
I would guess perp already had his family tied up when SS showed up. So SS would be concerned if he did anything, perp would have enough time to kill his child and his wife.