LOS ANGELES – A light drizzle had begun in south Los Angeles when the sound of a school bell unleashed a stream of students onto the pavement. Clad in grey skirts and purple polo shirts, the uniform at the all-girls public school, students climbed into school buses or scanned the scrum of cars hopefully for a parent arriving on time in the November rain.

Alexis Munoz – a 13-year-old with wavy hair and a smile threaded with braces – ambled away from the scene and up to a busy street. A white Jaguar sport utility vehicle came into view and pulled over, its spinning cameras and sensors hinting at an empty driver’s seat.