" Maybe they killed the dog and baby because they didn't want them left without care in the cruel world they were leaving behind." Hastings I think you are right.
Grim but it happens. Twenty five years ago a woman in SC strapped her two little boys into the child seats and rolled the car into the pond.
About 8 years ago a gal in Texas took her 5 kids, age 7 to age 1 year, and drowned them one-by-one in the bathtub.