After an excruciating 10 days without much to go on, authorities looking for Nancy Guthrie finally have a potential big break: video of an armed, masked person at her doorstep the morning she went missing. The black-and-white video captured by Guthrie’s doorbell camera, which the FBI and the Pima County, Arizona, Sheriff’s Department shared Tuesday , gives investigators clues that could help their search. “When you get video, it opens up many new avenues and details,” said Eric Draeger, a