A point of clarification- the CO theory was a very early one, the hydrogen Sulfide poisoning is the final cause given- after months of testing.
This was odd from the beginning- the SUV simply slowed down and crashed in to the left hand guard rail- a low speed crash. When Troopers approached the car, they saw the lady and her child unconscious, and the motor was still running. They broke a window, and were immediately overcome by fumes. Hazmat was called, they were decontaminated, but by the time they got to testing the air in the SUV, it was clean.