It should have been plain sailing for a South Korean ferry carrying hundreds of children and their teachers on an outing to the sub-tropical island of Jeju, an annual trip for Danwon High School.
The Sewol had 476 passengers and crew on board, including 339 children and teachers. It had an experienced captain, was navigating well-known waters and had passed its annual inspections since it was bought second hand in 2012 by Chonghaejin Marine Co. Ltd.
But prosecutors believe the vessel capsized after turning at too high a speed. Sixty-four people are known to have died and 238 are missing, presumed dead, mostly children.
In an arrest document, the captain was charged with undertaking an "excessive change of course without slowing down" while traversing a channel off South Korea's southwestern tip. He was also charged with negligence in evacuating passengers.
The sequence of known events however offers little clarity on why the ship should have turned at speed.
According to fishermen and others who navigate the tidal waters around Jindo island where the Sewol started to sink last Wednesday, the route followed by the ferry from the port of Incheon to Jeju was regularly used by ferries and larger vessels such as oil tankers.
There were few navigation risks in the main channel, they said. The Korean Meteorological Association said there was a 0.5 metre swell. It was cloudy, but there was no fog.
"The shores of the islands nearby drop straight down," said Hwang Wan-soon, captain of a 9.77 ton fishing boat who has 40 years' experience sailing in the area.
Han Sang-sik, head of the Jindo office of the Dadohae Haesang National Park - an area covering 1,700 islets - said the channel in the spot where the Sewol sank was 37-43 metres (122-142 feet) deep and the channel itself was 3 km (two miles) wide, offering plenty of room for manoeuvre.
"People living in nearby islands say fishing boats tend to avoid the area at full moon as the current is especially strong at that time," he said. There was a full moon the night before the accident.
But that should not have been an issue for the Sewol, with a gross tonnage of almost 7,000 tonnes and one of the largest passenger ferries in operation in Korean waters.
The accident happened when the ship made an abrupt turn and started to list sharply. That's when the ship was suspected of going too fast. It was not clear