Police have reportedly taken the hospitalized driver of a Spanish train into custody a day after a violent derailment killed at least 80 people and maimed dozens more.

The train, which hurtled off the rails and smashed into a security wall as it rounded a bend, was going so fast that carriages tumbled off the tracks like dominoes, according to eyewitness accounts and video footage obtained Thursday.

An analysis of video images suggests the train may have been traveling at twice the speed limit, or more, along that curved stretch of track. The unanswered question is: Why?

Spain’s government said two probes have been launched into the train’s derailment Wednesday night on its approach to this Christian festival city in northwest Spain, where planned celebrations in honor of one of Jesus’ disciples gave way to a living nightmare.

The train company Renfe said 218 passengers and five crew members were on board. Spanish officials said the speed limit on that section of track is 50 miles per hour.

Earlier Thursday, the regional government in Galicia confirmed that police were planning to question 52-year-old driver Francisco Jose Garzon Amo, who was admitted to Santiago de Compostela’s main hospital with unspecified injuries. At the time, investigators cautioned that possible faults in safety equipment were also being investigated.

Spain’s lead investigator in the crash, Judge Vazquez Taín, ordered detectives to question Amo, a 30-year employee of the state rail company who became an assistant driver in 2000 and a fully qualified driver in 2003. The company said Amo took control of the train from a second driver about 65 miles south of Santiago de Compostela.

Renfe’s president, Julio Gomez-Pomar Rodriguez, told Spain’s Cadena Cope radio network that the driver had worked on that route for more than one year.

The Interior Ministry raised the death toll to 80 in what was Spain’s deadliest train wreck in four decades. The Galician government said 94 others remained hospitalized in six regional hospitals, 31 of them — including four children — in critical condition.

The U.S. State Department said one American was killed in the crash and five others were injured. State Department spokeswoman Marie Harf said those numbers were “likely to change” and declined to elaborate.

“Today the American people grieve with our Spanish friends, who are in our thoughts and prayers,” President Barack Obama said in a statement.

In the morning, Prime Minister Mariano Rajoy, a native of Santiago de Compostela, toured the crash scene alongside rescue workers and went to a nearby hospital to visit the injured and their families. In the evening Spain’s head of state, King Carlos, and Queen Sofia, went to the same hospital dressed in black.

“For a native of Santiago, like me, this is the saddest day,” said Rajoy, who declared Spain would observe a three-day period of mourning. He said judicial authorities and the Public Works Ministry had launched parallel investigations into what caused the crash.

Eyewitness accounts backed by security-camera footage of the moment of disaster suggested that the eight-carriage train was going too fast as it tried to veer left underneath a road bridge.

An estimate of the train’s speed at the moment of impact using the time stamp of the video and the estimated distance between two pylons gives a range of 89-119 mph. Another estimate calculated on the basis of the typical distance between railroad ties gives a range of 96-112 mph.

While sections of the Spanish press pointed an accusatory finger at the train driver, Spanish authorities and railway safety experts cautioned that a fault in systems designed to keep trains traveling at safe speeds could be to blame.