A clearer picture started to emerge of the time around the capsize with the release by coastguards of a conversation between vessel controllers and the ship.
Witnesses have said the Sewol turned sharply before it began listing. It is still not clear why the vessel turned.
(Read more: Captain arrested in Korean ferry sinking)
It took more than two hours for it to capsize completely but passengers were ordered to stay put in their cabins.
According to the transcript, at 9.25 a.m. the controllers told the 69-year old Captain Lee Joon-seok to "decide how best to evacuate the passengers" and that he should "make the final decision on whether or not to evacuate".
Lee was not on the bridge when the ship turned. Navigation was in the hands of a 26-year old third mate who was in charge for the first time in the passage, according to crew members.
The transcript shows crew on the ship worried there were not enough rescue boats at the scene to take on all the passengers. Witnesses said the captain and some crew members took to rescue boats before the passengers.
Lee said earlier he feared that passengers would be swept away by the ferocious currents if they leapt into the sea, but he has not explained why he left the vessel.
Prosecutor Yang Joong-jin told a news conference in Mokpo, one of the centres for the investigation, that some of the crew said they had not received any safety training.
(Read more: South Korea ferry death toll rises, hope fades)
"We are trying to find out if there is additional negligence," Prosecutor Yang Joong-jin told a news conference in Mokpo, one of the centres for the investigation, speaking of the captain and crew.
When the captain and two crew were arrested on Saturday, they were detained by police for 10 days and prosecutors for a further 10. If the new extension request is granted, they could be detained for 30 days.
Anger and anguish
Yang said that prosecutors had also summoned 10 other people to give evidence, including other crew from the Sewol and officials from the ferry's owner, Chonghaejin Marine Co Ltd.
More divers managed to gain access to the stricken ship on Sunday as guide ropes were installed to help them through the tricky and fast currents in the area, although for many of those waiting in Jindo the recovery was still not quick enough.
Relatives of those listed as missing, but who are now presumed to be dead, clashed briefly with police when about 100 of them tried to leave the island by a road bridge to the mainland to take their protest to the capital city of Seoul.
Police blocked them and they later turned back.
(Read more: Scenes from South Korea's ferry disaster)
"Bring me the body," weeping mother Bae Sun-ok said of her child as she was comforted by two policemen at the bridge.
More than 500 parents of the schoolchildren and relatives of other people missing have spent four days and nights cooped up in a gymnasium in the port city of Jindo, which is the centre of the rescue operation.
Tempers have frayed over the slow pace of the recovery and frequent changes in information.
President Park Geun-hye was booed by some of the relatives when she visited the gym on Thursday.
Pupils at the school in Ansan, a gritty commuter town, set up shrines to the dead and posted messages for the missing.
The vice-principal of the school, who was on the ferry and survived the capsize, hanged himself outside the gymnasium in Jindo in another blow to the school and his body was discovered by police on Friday.
The sinking looks set to be the country's worst maritime disaster in 21 years in terms of loss of life.