This story was originally published by ProPublica , a Pulitzer Prize-winning investigative newsroom, and is republished here by permission. Sign up for The Big Story newsletter to receive stories like this one in your inbox. It was 4:32 p.m. and Mike Diaz was almost halfway through another punishing 24-hour shift when the call came over the ambulance radio. Nine miles away, a man had lost consciousness. “We’re en route from Palmdale Regional,” Diaz told the dispatcher, pushing away the thought of grabbing some food, as he flicked on the lights and sirens and sped off into the suburban maze of the Antelope Valley. He had worked as an emergency medical technician here in the northernmost part of Los Angeles County for over a decade, but he still experienced the same thrum of adrenaline on urgent calls. Lately, however, on January afternoons like this one, his excitement was overpowered by a sense of futility and dread.