Investigators believe either a tyre explosion of the van or its driver sleeping behind the wheel was the cause of its horrifying collision with a pickup truck in Chon Buri on Monday which killed 25 people.
Pol Lt Gen Jitti Rodbanyang, the Provincial Police Region 2 commander, said on Monday night at Bang Bung Hospital that the collision on Road 344 in Ban Bung district was most likely caused by one of the two factors.
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Police are collecting evidence to shed light on the cause of the crash, he added.
Their work might not be easy as Sumon Ieamsombat, who drove the van, was among the dead in the accident on Monday afternoon.
The van, with 14 passengers and the driver, was heading for Bangkok from Chanthaburi when it flew across a road dividing ditch and crashed into the pickup truck carrying 12 people in the opposite lane, causing fire on the two vehicles. Only two people survived and sustained minor injuries -- a woman sitting in the open cargo area of the pickup truck and a man on the last row of the van's seats.
The blast was believed to be due to the compressed natural gas cylinder in the van.
The vehicle belongs to Pattarapong Sueanak, who operates the Bangkok-Chanthaburi route under a concession of Transport Co, a state enterprise of the Transport Ministry.
Mr Pattarapong told Thai Rath Online on Tuesday that the NGV cylinder had been safely installed and insisted that the driver had a good rest before returning to the driver's seat.
The van arrived in Chanthaburi from Bangkok at 5am on Monday before making a return trip -- the last one -- at 11am, according to the van owner.
Rescue workers on Tuesday moved 25 bodies from Ban Bung Hospital to the Institute of Forensic Medicine of Police General Hospital in Bangkok for identity verification as they were totally burned.
Institute commander Pol Maj Gen Pornchai Suteerakune said forensic officials would try to identify the bodies by Tuesday and allow their families to take them for religious ceremonies on Wednesday.
The families are at the hospital waiting for the institute to release the bodies after their names have been confirmed.
One of the dead victims in the van was identified as Nuengruethai Modphai, who was on her way back to work in Bangkok after visiting her family in Chanthaburi.
After hearing the news of the accident, her mother Wimol rushed to the van station in Chanthaburi to check whether her daughter was in the vehicle from the camera footage there. She later went to Ban Bung Hospital and confirmed the identity of her daughter to forensic officials after seeing a piece of evidence.
"I'm shocked and saddened by what happened," Mrs Wimol told Thai Rath TV. "I told myself all the way from home to the hospital that it wasn't real."
"All agencies involved including van operators should check their vehicles and the readiness of drivers before each trip, especially during long holidays when the drivers have to make more trips," she said.
"State regulators must also do a better job," she added.