EARLY on a Sunday morning in March, a crowd of people hovered anxiously outside a modest Long Island home in Floral Park. A few of them had been there since before daylight — one since 3 a.m. — alternately dozing, pacing and peering through the windows of the house. By 9, those closest to the front door were starting to pound on it. Finally, the door opened a crack, and Mona Scavo, a tall woman with blond highlights, looked out at the crowd. “O.K., we’re going to stay calm, right?” she said in the friendly but firm tone of a kindergarten teacher.