Two days after Taiwan’s deadliest rail disaster in decades, investigators were working 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 for it.

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