SANTIAGO DE COMPOSTELA, Spain - By all accounts, the train was going way too fast as it curled around a gentle bend. Then in an instant, one car tumbled off the track, followed by the rest of the locomotive, which seemed to come apart like a zipper being pulled.
The derailment sent pieces of the sleek train plowing across the ground in a ghastly jumble of smashed metal, dirt and smoke.
But a day after Spain suffered its deadliest rail disaster in decades - which killed 80 people and maimed scores of others - one question surpassed all others: Why was the train moving so fast?
This image taken from security camera video shows a train derailing in Santiago de Compostela, Spain, on Wednesday. Spanish investigators tried to determine Thursday why a passenger train jumped the tracks and sent eight cars crashing into each other just before arriving in this northwestern shrine city on the eve of a major Christian religious festival, killing at least 77 people and injuring more than 140.
Investigators opened a probe Thursday into possible failings by the 52-year-old driver and the train's in-built speed-regulation systems.
Experts said one, or both, must be at fault for the disastrous Wednesday night crash of the train that was carrying 218 passengers and five crew members to Santiago de Compostela, a destination of Catholic pilgrimage preparing to celebrate its most revered saint.
Instead, this stunned city of nearly 100,000 converted its sports arena into a shelter for the dead and the grieving.
"All Spaniards feel the pain of the families," said Spain's head of state, King Juan Carlos, as he and Queen Sofia met hospitalized survivors of the crash 2.5 miles (4 kilometers) south of Santiago de Compostela. The royal couple dressed in funereal black.
"For a native of Santiago like me, this is the saddest day," said Prime Minister Mariano Rajoy, who toured the crash scene and declared a national three-day mourning period.
The regional government of Galicia, in northwest Spain, said 94 people remained hospitalized, 31 of them in critical condition, including four children. The U.S. State Department said one American died and at least five others were hurt but cautioned that those figures could be revised upward.
Many victims suffered severe burns as the train's diesel fuel ignited a fire that caught some passengers trapped in mangled upside-down carriages. Emergency officials took DNA samples from the most heavily burned or the unconscious in an effort to identify both the living and the dead.
Rafael Catala, a senior transport official in Spain's Development Ministry, told radio network Cadena SER that the train appeared to be going much faster than the track's speed limit of 80 kph (50 mph) as it approached the city.
Breathtaking footage of the crash captured by a railway security camera showed the moment when the eight-carriage train approached a left bend beneath a road bridge at a seemingly impossible speed. An Associated Press analysis of the video indicated the train hit the bend going twice the speed limit or more.
Using the time stamp of the video and the estimated distance between two pylons, the AP calculated that the train was moving in a range of 144 to 192 kph (89 to 119 mph). Another estimate calculated on the basis of the typical distance between railroad ties indicated its speed was between 156 kph and 182 kph (96 to 112 mph).
The anonymously posted video footage, which the Spanish railway authority Adif said probably came from one of its cameras, shows the train carriages buckling and leaving the tracks soon into the turn.
Murray Hughes, consultant editor of Railway Gazette International, said a diesel-powered unit behind the lead locomotive appeared to derail first. The front engine quickly followed, violently tipping on to its right side as it crashed into a concrete wall and bulldozed along the ground.
In the background, the rear carriages could be seen starting to decouple and coming off the tracks. The picture went blank as the engine appeared to crash directly into the camera.
After impact, witnesses said, a fire engulfed passengers trapped in at least one carriage.
"I saw the train coming out of the bend at great speed and then there was a big noise," eyewitness Consuelo Domingues, who lives beside the train line, told The Associated Press. "Then everybody tried to get out of the train."