A message is seen on a guardrail in front of the City Hall Station to mourn the deaths of those who were killed in a car crash in central Seoul on Monday (Yonhap)

Police on Tuesday opened an investigation into a 68-year-old man for a car accident late Monday that claimed the lives of nine people and left four injured in central Seoul.

They said they had mobilized forensic scientists and investigators to determine the cause of the crash, which the driver says was caused by a vehicle fault, a claim experts have cast doubt on.

Police are seeking a warrant to arrest the driver on suspicion of negligent driving resulting in death, according to Chung Yong-woo, a senior police officer at Namdaemun Police Station, during a briefing to reporters.

The driver claimed that the vehicle went out of control due to a sudden unintended acceleration. On the other hand, local automobile experts believed that the deadly accident was caused by driver negligence.

"Police will conduct the investigation as promptly as possible to prevent any destruction of evidence," Chung said.

The remarks came following the crash, which took place at an intersection near Seoul City Hall at around 9:27 p.m. on Monday, when a Genesis sedan plowed into pedestrians waiting to cross the road. The vehicle was driving on the wrong side of the road and collided with two cars before hitting the pedestrians, according to police.

The driver is reportedly a bus driver with over 40 years of experience in Ansan, Gyeonggi Province, who obtained his bus drivers’ license in 1974, according to reports.

"It's difficult to provide additional information at this point as the investigation is still ongoing, but it seems like the deceased and the injured were hit by the car," Chung told The Korea Herald.

Some six people died at the scene, while three were transported to a hospital but were later pronounced dead. Those killed included four colleagues from a nearby bank, all men in their 40s and 50s, and two employees of the Seoul Metropolitan Government, according to reports. Among the four injured, one was seriously injured, while the others sustained minor injuries.

Vowing a "strict and prompt" probe into the case, Chung also dismissed the driver's claim that the accident happened due to "sudden unintended acceleration," but said they would request a thorough analysis of the car by the National Forensic Service to verify his claim. Authorities will also look into the speed of the vehicle at the time of the accident.

The driver was not under the influence of alcohol or drugs at the time of the accident. However, the crash has rekindled a recent debate about whether older people should be subjected to a conditional license system for "high-risk drivers."

In addition, officials plan to question the driver's wife, who was in the car at the time of the accident, as well as reconstruct the scene of the crime by using CCTV footage, black box data and witness statements to establish the exact circumstances of the crash.

Experts say the chances of a sudden unintended acceleration due to mechanical malfunctions with the vehicle are low.

While it's crucial to leave all possibilities open regarding a car crash, Lee Ho-geun, an automotive engineering professor at Daedeok University, said that the circumstances point to negligence behind the wheel.

"Drivers should primarily focus on minimizing the risk of harm in a sudden unintended acceleration by steering the vehicle away from traffic, but the driver, in this case, ran into a congested metropolitan street, causing casualties," Lee told The Korea Herald.

Kim Pil-soo, an automotive engineering professor at Daelim University, said that driver error likely caused the crash.

"Drivers experiencing a sudden unintended acceleration in a car accident that happens within five to six seconds usually struggle in accurately remembering and recounting the sequence of events due to the unexpected shock," Kim pointed out.

"However, the driver got out of his car (after the crash), and witnesses of the accident say the driver checked the car and fled the site, meaning the incident couldn't have occurred due to uncontrolled acceleration of a vehicle, because the driver knew he was at fault and left the scene," Kim said, citing local reports.

Park Chul-wan, a professor of automotive engineering and secondary batteries at Seojeong University, said the driver might be claiming that his car unexpectedly sped up on its own to avoid being held accountable for causing the accident.

"In the event of a sudden acceleration causing a car to stop, the transmission system (of the vehicle) continues to deliver power to the wheels as the engine continues to run. In such a case, the wheels continue to spin and make loud noises. But that didn't happen (during Monday's accident)," Park told The Korea Herald.