I wonder if H & W had separate cars, each equipped with a child safety seat and, apparently, W puts the baby in H's car but H thinks W put the baby in W's car.
Any other way, and this makes no sense to me.
That’s how I figured it. The confusion was that one of them put the baby in the other ones car, and thought they understood they were responsible for the child. The baby made no noise, and wasn’t discovered. Tragic. Both parents will never get over this. How horrible.
Normally when children are this young, they are in rear-facing child seats that have separate bases. You strap the baby into the child seat outside the car, and snap it into the base in the back seat.
For the person to have left the child in the car, they would have had to miss a car seat in the back when normally there would be just a base.