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and the stunning outcome would tear pam's family apart. here's keith morrison with "before midnight." >> reporter: a few minutes after sunrise on the morning of november 4th, 2014, david zimmerman rose from his bed in a quiet suburb of bloomington, illinois. eager to dispose of the small worry that had been nagging at him all night, he padded across the room to his bedroom door. >> i woke up and walk out into the kind main hallway that we have and the lights were still on. >> reporter: the lights he'd left on when he went to bed. which meant what? david was 17 years old. the eldest of pam zimmerman's three children. they, not uncommonly, left the lights on for their mom when she worked late at her financial planning business. or when she stepped out with her new man. typically, when she got home, she turned the lights off. but this tuesday morning -- >> her bedroom is dark, and it