What drove Steve Nunn murder his ex-fiancee 20/20 : Season 34 Episode 14

A young girl drowns in her backyard pool, and her young step brother blames his mother after police rule it an accident. However, the mother contends that her son was coached and his inconsistent testimony of the events surrounding the drowning cannot be trusted. She is eventually convicted of first-degree murder by a jury in less than two hours, though she continues to appeal her case.