While a motive in the Annunciation School mass shooting remains under investigation, Alex Perez has the new video showing the chaos inside the church as gunfire erupted during Mass and the father of the 8-year-old killed in the attack speaks out; Mary Bruce has the latest on the dozens of workers who walked out and the four top officials that resigned in protest at the Centers for Disease Control and Prevention following the ousting of the agency’s director; Victor Oquendo has details on the horrific alligator attack in New Orleans that police say has left a missing 12-year-old boy dead; and more on tonight’s broadcast of World News Tonight with David Muir.

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