Prosecutor Yang Jung-jin of the joint investigation team says two helmsmen and two members of the steering crew were detained Saturday. Eleven other crew members, including the captain, were arrested previously.
They are accused of negligence and of failing to help passengers in need as the ferry Sewol sank April 16. The captain initially told passengers to stay in their rooms and took half an hour to issue an evacuation order, by which time the ship was tilting too severely for many people to get out.
Ten days after the sinking, 187 bodies have been recovered and 115 people remain missing.