The driver of a Spanish train that derailed at high speed killing 78 people has been released from hospital, and is now being held on suspicion of negligent homicide, Spain's Interior Minister has said.

Jorge Fernandez Diaz announced on Saturday the development in the case against Francisco Jose Garzon Amo, who previously had been detained on suspicion of recklessness following Wednesday's crash in Santiago de Compostela.

"There is rational evidence to lead us to think that the driver could have eventual responsibility," the minister told reporters at the city's police station.

Garzon, 52, will appear before a judge by Sunday evening at the latest to answer questions about what went wrong.

Blame has increasingly fallen on the driver, with the country's railway agency saying it was his responsibility to brake before going into the high-risk curve where the train tumbled off the rails and smashed into a wall.

Unidentified bodies

But it is still not clear whether the brakes failed or were never used, and the driver has remained silent so far.

A blood-soaked Garzon was photographed on Wednesday being escorted away from the wreckage, at first by civilians who had hurried to the scene of the accident and then by police.

Survivors and families of victims from Spain's deadliest train crash in decades were desperate for answers three days after the eight-carriage, high-speed train derailed on a sharp bend, slamming into a concrete wall.

Several bodies were still unidentified and dozens of injured remain in hospital in serious condition.

Officials are looking into whether the accident was the result of human error or a problem with the train, the track or the security system that controls speed on the railway.

Source: Al Jazeera and agencies