Three major criminal cases dominate this week's Dateline coverage: Lindsay Clancy's defense team argues she suffered undiagnosed postpartum psychosis when she killed her three children in Massachusetts; Luigi Mangione pleads guilty to federal stalking charges in the UnitedHealthcare CEO shooting while his lawyers fight state murder charges as double jeopardy violations; and the trial begins for one of three defendants accused of murdering Microsoft employee Jared Bridegan. Plus, an ATF expert explains ghost guns and their investigative challenges. Lindsay Clancy's family testified she begged for mental health help throughout late 2022, reported suicidal ideation daily in December, and told her mother and husband she had thoughts of harming her children before the January 2023 killings.