The driver of a train that derailed in northwestern Spain has been formally detained by police accused of “recklessness”.
The train derailed two miles south of Santiago de Compostela in Galicia, north-west Spain, injuring more than 100 people and killing 78 – revised down from the 80 figure reported by police earlier.
National Police Chief for the Galicia region, Jaime Iglesias, said driver Francisco Jose Garzon Amo was arrested in the hospital where he is recovering and would be questioned "as a suspect for a crime linked to the cause of the accident".
When asked at a press conference earlier today why Garzon, who is being guarded by police, was being detained, Mr Iglesias said: "For recklessness."
The 52-year-old driver cannot yet testify because of his medical condition, the police chief said, but his condition is not believed to be serious.
Earlier it was reported that investigators are focusing on the key question of why the train was going so fast – looking into possible failings by the 52-year-old driver and also the train's in-built speed-regulation systems.
Experts said one, or both, must be at fault for Spain's deadliest rail disaster in decades. Rafael Catala, a senior transport official in Spain's Development Ministry, said the train appeared to be going much faster than the track's maximum speed of 50mph as it approached the city.
"The testimony of the driver will help us identify the causes," Catala said.
Sections of the Spanish press pointed an accusatory finger at the driver, with many newspapers publishing excerpts from his Facebook account where he boasted of driving trains at high speed. The account was closed early on Thursday.
But government officials and railway experts cautioned that a fault in systems designed to keep trains at safe speeds could be to blame. Jose Antonio Santamera, president of Spain's College of Civil Engineering, said one of the train's fail-safe mechanisms could have failed.
"The security system will detect any fault of the driver, (for example) if he has suffered a blackout and does not answer calls, and then starts the train's security systems. So I almost rule out human error," he said.
He said the crash happened at a point where one speed-regulating system gave way to another, suggesting a possible failure at the handover point.
The train involved, made by Bombardier and Talgo, was a series 730 that Renfe uses for its Alvia service, which is faster than conventional trains but not as fast as the AVE trains that criss-cross Spain at even higher speeds.
The train was built in 2007-2009, but remodelled in 2012 to use diesel, and is designed to operate on conventional and high-speed tracks that make use of two different types of safety systems that are meant to regulate excessive speed.
On high-speed lines, trains use the European Train Control System, or ETCS, system, which automatically slows down a train that is going too fast.
On slower lines, trains operate under an older system called ASFA, a Spanish acronym for Signal Announcement and Automatic Braking, which warns the driver if a train is moving too fast but does not automatically slow it down.
At the site of the disaster, just 3km before reaching the Santiago de Compostela station, the train was passing through an urban area on a steep curve. At that point of the track, two railway experts said, it uses the older ASFA safety system.
Professor Roger Kemp, a Fellow of the Royal Academy of Engineering in Britain, said in an e-mailed comment: "As the driver was leaving the high-speed line to join a much slower route before entering the station, there must have been at least prominent visual warnings to reduce speed, if not audible warnings and an electronic speed supervision system."
Local media reported that railway union representatives had questioned whether a high-speed train should have been adapted to run on a track with curves that had been designed for lower-speed trains.
A source close to ADIF said the safety system was apparently working correctly and a train had passed an hour earlier with no problems.