Francisco Jose Garzon Amo, the train driver in last week’s crash in Spain, was talking on the phone when it derailed, investigators say.
The train was travelling at 153 km/h (95 mph) at the time, investigators at the Court of Justice of Galicia said.
Francisco Jose Garzon Amo was speaking to members of staff at the state-owned railway company, Renfe, they added.
Crash investigators had opened the train’s “black-box” data recorder to find the cause of the crash, which left 79 people dead.
Moments before the accident the train was travelling at a speed of 192 km/h (119 mph), the court said in a statement.
Investigators say the brakes were activated shortly before the crash.
The speed limit on the sharp bend where the train derailed was set at 80 km/h (49 mph).
“Minutes before the train came off the tracks he received a call on his work phone to get indications on the route he had to take to get to Ferrol. From the content of the conversation and background noise it seems that the driver consulted a map or paper document,” a court statement said.
Francisco Jose Garzon Amo is suspected of reckless homicide, but he has not yet been formally charged.
He was released from custody in Santiago de Compostela, where the crash occurred, on Sunday but remains under court supervision.
He must appear before a court once a week and was not allowed to leave Spain without permission.
Francisco Jose Garzon Amo’s passport has been surrendered to the judge and his licence to drive a train has been suspended.
Under Spanish law, his legal status is that he is suspected of being involved in 79 counts of reckless homicide but has not been formally charged.
But officials said he had admitted negligence by being careless when rounding a bend too fast.
All eight carriages of the train careered off the tracks into a concrete wall as they sped around the curve on the express route between Madrid and the port city of Ferrol on the Galician coast.
On Monday, a mass was held in the cathedral in Santiago de Compostela.
PM Mariano Rajoy, along with the heir to the Spanish crown, Prince Felipe, and his wife Princess Letizia, joined the grieving families and local residents in the cathedral as the city’s archbishop prayed for the dead.