HEREFORD, Ariz.--Last July 6, Mercedes Maharis awoke at 11 p.m. to the roar of a Border Patrol helicopter hovering outside her living room here, two miles north of the Mexican border. It was pitch black outside. The chopper blades pounded so hard that her windows shook as if under artillery bombardment. She opened the door and heard people screaming and running as the chopper herded them off the hill toward three Border Patrol trucks below. In her nightgown, shaking with fear, Ms. Maharis grabbed her camera and filmed the scene. "I had to film it because nobody would believe it,"...