MOKPO, South Korea (AP) — A prosecutor says that the third mate steering a South Korean ferry at the time of a major accident was navigating those waters for the first time.

Senior prosecutor Yang Jung-jin told reporters that the 25-year-old mate was steering the ship as it passed through an area with lots of islands clustered close together and fast currents.

The ferry sank Wednesday. More than 270 people are still missing.

Yang says that another mate usually took controls through the area. But because heavy fog caused a departure delay, the third mate was steering the ship through the waters. Yang says investigators have not confirmed whether the ship was going faster than usual.

Police have arrested the ferry captain on suspicion of negligence and abandoning people in need.