An illegal foreign worker has been detained as a second suspect in Taiwan's worst train derailment in seven decades in Hualien County on the east coast that killed 50 people and injured more than 200 others, authorities said Thursday.

Chief prosecutor of the case at the Hualien District Prosecutors Office Chou Fang-yi told reporters that two men are suspected of causing the April 2 disaster and the court approved on Thursday afternoon their request to detain the second suspect, who she said is a foreign worker from Vietnam who has been in Taiwan illegally.

Workers remove a derailed train from a tunnel in Hualien County in eastern Taiwan on April 6, 2021. (Central News Agency/Kyodo)

The main suspect, Lee Yi-hsiang, has been detained for further questioning since Sunday. The court has seized Lee's assets to prevent him from transferring his personal assets and those under his two companies that are subcontractors of the Taiwan Railway Administration.

As Lee also serves as a construction site manager for the TRA, rail authorities say Lee lied about his identity to circumvent the law prohibiting holding of both positions, construction company owner and construction site manager.

Authorities also found that Lee lied about inspecting the construction site alone. Surveillance camera footage showed that more vehicles and other people were at the site on the day of the accident, even though he TRA had ordered all construction work to be halted during the four-day Tomb Sweeping Festival.

Investigators said Lee was not alone, but instead with a man caught on surveillance camera with him in the crane truck loaded with waste tires. Prosecutors identified the passenger as the illegal worker from Vietnam.

Lee is the driver of a crane truck that rolled down a slope on April 2 and caused the accident. Railway authorities suspect that the truck was parked without the emergency brake engaged.

The Transportation Safety Board Chairman Young Hong-tsu said on Tuesday that the brakes of the truck had been modified without the certification of the manufacturer, and that its engine had been turned off before it rolled down the slope.

While it is unclear how the truck rolled down the hill beside the track, the board found that before that happened, the truck ran off the dirt road at a turning point where it got stuck in roadside bushes and its engine stalled.

Young told reporters at the legislature on Thursday that more evidence has been secured, including an audio and video recording between Lee and the illegal foreign worker inside the truck. However, Young declined to reveal details of their conversation.

Prosecutors seek to determine whether Lee and the illegal foreign worker tried to use another on-site crane truck to free their truck from the roadside bushes.

Meanwhile, trains in Taiwan mark the seventh day of the accident on Thursday by sounding their horns.

Trains passing the accident site did so for 30 seconds, and at least 120 trains did so or five seconds at 9:28 a.m., the time of the accident.

Taiwanese believe that on the seventh day, the spirits of a deceased would return to the house of that person's family and religious rituals must be performed to welcome the dead.

Among the 50 people who died were a 5-year-old girl, two American women in their 20s and a Frenchman who would have turned 28 two days after the accident. The train driver, 32, and his 31-year-old assistant also lost their lives.

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