Both the father and his son died bec they inhaled chemicals that is not good for the body. (Not sure if its benzene though). A running engine with aircondition operating emits chemicals and byproducts during the process. The chemical it emits is very harmful to our body. Assuming they are in a enclosed parking area, there is unsufficient air flowing thus these chemicals circulate around the room and go back inside the car. This is why even the chemical is emitted outside the car, because the room lacks ventilation, it will go back inside. Once it enters the car, this is the time the people inside inhaled it and cause them to have impairments and eventually death because of the huge volume being taken to our body. That's is why we should not stay long inside the car especially in closed area because it can cause dizziness and sometimes even nervous system problem.