This is closed-circuit television footage of the Sewol-ho ferry on the day of her departure from Incheon harbor.
Vehicles are loaded onto the vessel, one after another, 30 more automobiles than was previously declared.
The last vehicle is loaded, and just three minutes later, the ferry sets sail.
Experts say that's not enough time for the crew to correctly secure the freight.
"We assume the crew tied only two ropes instead of four. They may have just tied things up loosely before the departure."
Japanese researchers carried out a simulation to find out what happens when freight in a vessel is not fastened appropriately.
They made a model one-fiftieth the real size of the Sewol-ho and raised the center of mass in consideration of the fact that the Sewol-ho ferry had been renovated recently.
First, they ran the simulation without any cargo.
Sailing at five kilometers per hour, the same speed as the Sewol-ho, when turned right, the model sharply leaned outward toward the turn, due to centrifugal force, but did not capsize.
Next, they added some weight to the ship, to account for the mass of the freight and fastened it tightly.
When given an abrupt turn, the model again tilts sharply to one side, but is able to balance back without falling.
Then they tried again, this time with the same amount of weight, but without fixing it properly.
At first, it seemed to be navigating smoothly, but as soon as it makes a sharp turn, it listed to one side and capsized in a matter of seconds.
"When a vessel makes a sharp turn without its freight properly fastened, a heavier centrifugal force is applied, causing the vessel to list more outward. In extreme cases, the ship can capsize."
It is common for the captain or the chief mate to take at least an hour to make sure all cargo is secured tight before setting sail.
Japanese experts say there was no time to do that in the Sewol-ho's case last week, which leads them to believe that improper fastening of the freight may have been the main cause of the accident.
Sohn Jung-in, Arirang News.