Adopted or not children will eventually go their own way, so no, adoption isn't relevant in whatever a child's future is once they become an adult.
That crime scene was a bloodbath, whereas a person used to shooting wouldn't have created such a scene. It was frenzied shooting, proof enough that Sheila hadn't been used to using guns.
Or it was frenzied shooting because Jerermy, an expert marksman, made it look as if Sheila, who wasn't, did it.
Re adoption. We receive our genetics from our biological parents/families, not our parents by adoption. What we pick up from those is learned behaviour. There are some behaviours we'll have no interest in learning.