Taiwanese authorities are questioning a man whose parked truck slid down an embankment at a construction site beside the entrance of a train tunnel, causing a train to derail.
Fifty-one people, including the driver of the train, were killed, and at least 180 others injured in Friday's accident in the eastern county of Hualien.
Work to move the train started on Saturday but is being hampered as the first five cars of the eight-car train that entered the tunnel are severely damaged.
The authorities expect it will take about seven days to move all the cars and fully resume train service.
Many family members of the victims visited the accident site and called out the names of their loved ones.
The authorities say the truck slid about 20 meters before the train crashed into it and derailed.
They suspect the truck's emergency brake was not properly engaged or was disabled.