SEOUL, South Korea (AP) — All 15 people involved in navigating the South Korean ferry that sank and left more than 300 people dead or missing are now in custody after authorities on Saturday detained four more crew members, a prosecutor said.

Yang Jung-jin of the joint investigation team said two helmsmen and two members of the steering crew were taken in on preliminary arrest warrants issued late Friday. Eleven other crew members, including the captain, had been formally arrested earlier.