After poisoning her husband, daughter AND daughter-in-law with arsenic, "red collar Black Widow" killer Audrey Marie Hilley vanished without a trace. By the time police caught up with her she had created a fake identity, married a new husband, faked her own death and then come back to town pretending to be her (fictional) twin sister. This episode is a deep dive into the psychology of a cold-blooded killer who looks like the girl next door.
SOURCES:
JUSTICE STORY: A black widow's tangled web
Audrey Marie Hilley Poisons Husband, Daughter Before Escaping Prison | Crime News
Fugitive fakes death and returns as twin sister - UPI Archives
ABC has its own sicko movie in 'Wife, Mother, Murderer' – Baltimore Sun