Sibling Rivalry.....That is what fueled the anger and jealousy that caused an explosion that no one saw coming...What would make someone so angry to commit a heinous crime against a loved one? Was envy the green monster lurking behind closed doors? or was someone just taken over by so much hate, that it literally turned them into the monster that even scared them when they looked in the mirror.

Sources:

https://thecinemaholic.com/jossie-merrifield-murder-where-is-sandra-merrifield-now/

https://www.themidwestcrimefiles.com/post/the-merrifield-sisters