Investigators said yesterday that they were able to reconstruct 98 per cent of the moments - even seconds - leading up to the Taroko Express train crash on Taiwan's mountainous east coast.
This was carried out based on two memory cards from the dashboard camera of the construction truck that the train had crashed into on the railway track last Friday.
The second memory card was located on Wednesday, days after the first card and the camera were found.
The truck was said to have slipped off a work site next to the railway track just minutes before the express train travelling at more than 120kmh rammed into it and derailed, killing at least 50 people.
"We have obtained audio recordings at the construction site, including a key conversation that happened (after) the truck was entangled in some bushes," Taiwan Transportation Safety Board (TTSB) chairman Young Hong-tsu told lawmakers yesterday.
Dr Young confirmed that there were two people at the construction site - truck owner and construction manager Lee Yi-hsiang, and a Vietnamese migrant worker known as "A-hau", whom Mr Lee had hired illegally.
A-hau had been on the run from immigration officers for almost five years, police said.
Mr Lee claimed that he had gone to check on the construction progress alone last Friday morning when the tragedy took place, but highway surveillance cameras showed him driving A-hau to the site in his truck, which was loaded with old tyres.
"A couple of other construction trucks followed them to the site as well," said Dr Young.
Mr Lee's truck allegedly tumbled down to the train tracks after getting caught in the vegetation, but the TTSB is still puzzled as to how it came loose.
Local media quoted anonymous sources as saying that the truck had fallen in the way of the 408 Taroko Express train when Mr Lee was trying to get it out of the bushes with an excavator, but the claim has not been confirmed by the authorities.
The recording which the TTSB reviewed was a discussion between Mr Lee and A-hau that lasted about 10 seconds.
According to Dr Young, the two were debating over how to deal with the truck after it fell onto the train tracks, as well as the truck's condition.
Although Dr Young believed his team was able to piece together 98 per cent of what had happened at the construction site, "prosecution will be handling the remaining 2 per cent", he said.
A-hau was arrested by police on Wednesday night.
Hualien prosecutors filed to detain him yesterday to prevent him from destroying relevant evidence.
Mr Lee and A-hau have been listed as co-defendants but they have not been formally charged, said Ms Chou Fang-i, chief prosecutor for the Hualien District Prosecutors Office.
The number of people subpoenaed for the investigation is growing, Ms Chou added.
The government is also waiting for the prosecution's investigation to be concluded.
Deputy Transportation Minister Wang Kwo-tsai said: "If Lee Yi-hsiang caused the truck to slide onto the tracks as he was trying to pull it (up with an excavator), we'll have to ask prosecution to discuss if this is death by negligence or indirect but intentional homicide."
Meanwhile, memorial services for those who perished on the packed train were held in their home towns Hualien and Taitung in eastern Taiwan yesterday, which marked the seventh day of their death.
It is a time known as "First Seven" in Taoist funeral traditions. Taoists believe that the dead return to visit their loved ones on the seventh day of their death.
All trains belonging to the Taiwan Railways Administration, which operates the Taroko Express service, yesterday sounded their horns for five seconds at 9.28am - the time at which the train had crashed - in a sign of respect for the victims and survivors.