GWANGJU, South Korea — Prosecutors Monday demanded the death penalty for the captain of the South Korean ferry that sank in April, killing 304 people, most of them teenage students, in the country’s worst peacetime disaster in decades. [...] the crew members did not take any of the steps they could have easily taken, such as activating the evacuation alarm bells, before they fled the ship to get onto the first coast guard boats arriving at the scene, prosecutors said.