Whether these incidents are an accident, I do not believe matters.
A person must still be held accountable for the loss of life. Yes, I know they are hurting, but they are responsible, and a serious failure occurred.
However, in this case, it seems like this was planned, and if that is proven to be the case, this man should be executed IMO, and they can do it by putting him in a hot car. Let him learn how it feels first hand.
There are homicides where I believe the perpetrator should be put to death in the same manner as the person they killed. This would be one of those times.