HUALIEN, Taiwan – Two days after Taiwan's deadliest rail disaster in decades, investigators were working Sunday to determine why a truck had slipped downhill from a construction site into the path of an express train, resulting in the collision and derailment that killed dozens of people.

The operator of the crane truck, Lee Yi-hsiang, was ordered detained Sunday by a judge, who reversed an earlier decision to grant him bail. Lee, who has not been charged with a crime, told reporters he had caused the crash and said he would take full responsibility.

"I hereby express my deep regret and my sincerest apologies," Lee said, his voice choking as he bowed in apology.

But investigators were still trying to determine whether Lee had neglected to use the emergency brake or whether the truck had malfunctioned in some way. Lee told reporters Saturday that he had engaged the brake.

Officials said they were also trying to determine when the driver of the train applied the brake before the collision.

Officials said Sunday that 50 people had been killed in the crash of the eight-car Taroko Express, which derailed and slammed into a tunnel wall after hitting the truck Friday. The train was packed, carrying 498 people on the first day of a long holiday weekend.

Authorities had previously put the death toll at 51. Identifying victims has been a slow, difficult process, and emergency personnel Sunday were still trying to extricate wreckage from the tunnel and recover the victims' remains. Thirty-seven survivors were still hospitalized Sunday.

Some survivors and relatives of the dead have shown more grief than anger. Taiwan's last serious train crash, in 2018, was found to have been caused by driver's negligence, but initial impressions were that Friday's collision was more like a freak accident.

Some family members said they did not want to assign responsibility for the disaster before the government had finished its investigation, which authorities said would take about two months.

"I don't want to blame anyone," Wu Ming-Yu, 68, said Sunday as she sat with family members under a tent at a funeral home in Hualien, a city south of the crash site on Taiwan's East Coast. They were waiting for a mortuary makeup artist to finish work on the body of Wu's daughter, Huang Chiao-ling, a 35-year-old nurse who had been on her way to see her family.

The construction project had been commissioned by Taiwan's transportation ministry to improve the safety of the slope near the crash site, which occurred on a mountainside on the Pacific Coast. It was part of a six-year plan to enhance railway safety in Taiwan. The crane truck operator was also the project's site manager.

"It's ironic and very unfortunate," said Yusin Lee, a professor of civil engineering and director of the Center for Railway Studies at National Cheng Kung University, in the southern city of Tainan. "It's a reminder that even when we have safety-targeted construction projects, we still have to keep safety in mind."