A mom who says her 7-year-old pulled the trigger. And a medical examiner who speaks for the dead.

In suburban Boston, years after the death of a pregnant 23-year-old was ruled a suicide, the FBI arrest a former local detective for her murder. In Lake County, Florida, a mom on trial for her husband's murder is raising a wildcard defense: her daughter did it. And Dr. Mary Jumbelic answers our question: how can medical examiners reach different conclusions in the same cases?

NBC Boston's coverage of Sandra Birchmore's case

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