An express bus carrying 24 people fell off an elevated motorway into a construction site while trying to avoid colliding with other vehicles near Incheon Bridge, killing half of the passengers and injuring 12 others.
Police said the bus, heading to South Korea's main gateway Incheon International Airport west of Seoul, seemed to have lost control while trying to dodge a subcompact car and a one-ton truck which had crashed moments earlier.
On Sunday, police inspected the scene of the accident, trying to find out its cause and other details, including how the bus hurtled through a guardrail and then fell off the motorway.
About 30 families of the dead and the injured witnessed the police investigation.
"Based on today's inspection, we will throughly investigate into the cause of the accident," police said.
Police said they planned to book the drivers of the bus and the subcompact in violation of traffic laws. They said the bus driver was responsible for not having enough safety distance with the car ahead.
They have been investigating whether the driver of the broken car parked on the highway took enough safety measures such as turning on the emergency blinker signal and whether the bus secured enough safety distance.
They took the blood sample of the bus driver to check whether he had been intoxicated.
The death toll was higher than expected, because many of the passengers reportedly unfastened their seat belts, as the bus, which had departed from the southeastern port city of Pohang early Saturday, was near to its final destination, police said.
The 21.38-kilometer Incheon Bridge is South Korea's longest. It opened to traffic last October to connect Yeongjong Island, where the airport is located, and the Songdo free economy zone in the city's west coast.