The train carrying tourists to Portugal veered off the tracks and smashed into a pillar in the town of O Porriño Friday, killing its Portuguese driver as well as a US passenger and two Spaniards, and leaving 49 others injured.
Routine maintenance work was being carried out in the area, forcing it to divert to a secondary track where the speed limit was just 30 kilometres an hour, O Porriño mayor Eva Garcia de la Torre said at the weekend.
But information from the train's black boxes revealed that "the train was going at 118 kilometres per hour (73 mph) when it derailed," said the high court of Galicia where the accident happened and which is investigating the crash.
"The driver received and notified he had received (by pressing a button) two L1 notices, which indicate the need to reduce speed," it added in a statement.
But the court said it had yet to determine why the train, which belonged to Spain's rail company Renfe but was on loan to its Portuguese counterpart Comboios de Portugal, was going too fast.
It added that the body of the Portuguese train driver would be repatriated after he was formally identified.
The other three who died were the train conductor, a 23-year-old passenger and a US tourist.
While some of the injured are still in hospital, none are critical.
Spain's Public Works Minister Rafael Catala said Monday he wanted the presidents of Renfe and Adif, which manages the country's railway tracks, to appear before a parliamentary commission to ensure "transparency" in the accident inquiry.
Speeding was the cause of one of Spain's worst rail disasters in 2013, also in Galicia.
Some 80 people were killed and another 144 injured when a high-speed train slammed into a concrete wall on the outskirts of Santiago de Compostela.
The train was approaching a curve at more than twice the speed limit on that piece of the track.
The driver in that accident has been charged with negligent homicide, and an investigation is due to be reopened to determine if Adif was also partly responsible.