The driver was on the phone with a colleague and apparently looking at a document as his train barrelled ahead at 95 mph, almost twice the speed limit.
Suddenly, a notorious curve was upon him. He hit the brakes too late.
The train, carrying 218 passengers in eight carriages, hurtled off the tracks and slammed into a concrete wall, killing 79 people.
Today, investigators looking into the crash announced their preliminary findings from analysis of the train's data-recording "black boxes," suggesting that human error appears to be the cause of Spain's worst railway disaster in decades.
The derailment occurred near Santiago de Compostela, a city in northwestern Spain, late last Wednesday. Some 66 people injured in the crash are still hospitalised, 15 of them in critical condition.
The accident cast a pall over the city, which is the last stop for the faithful who make it to the end of the El Camino de Santiago pilgrimage route that has drawn Christians since the Middle Ages. The crash occurred on the eve of annual festivities at the shrine, which subsequently were cancelled.
The disaster also stunned the rest of Spain, with Spanish royals and political leaders joining hundreds of people in Santiago de Compostela's storied 12th-century cathedral Tuesday evening to mourn the dead.
According to the investigation so far, train driver Francisco Jose Garzon Amo received a call from an official of national rail company Renfe on his work phone in the cabin, not his personal cellphone, to tell him what approach to take toward his final destination.
The Renfe employee on the telephone "appears to be a controller," a person who organizes train traffic across the rail network, said a statement from a court in Santiago de Compostela, where the investigation is based. "From the contents of the conversation and from the background noise it seems that the driver (was) consulting a plan or similar paper document."
The train had been going as fast as 119 mph shortly before the derailment, and the driver activated the brakes "seconds before the crash," according to the statement. The speed limit on the section of track where the crash happened was 50 mph.
Authorities have said that a high-tech automatic braking program called the European Rail Traffic Management System was installed on most of the high-speed track leading from Madrid north to Santiago de Compostela, the route Garzon's train took. But the cutting-edge coverage stops just 5 kilometers south of where the crash occurred, placing a greater burden on the driver to take charge.