* Worst rail disaster in decades killed 79 people
* Excessive speed main cause of accident - judge
* Officials should have foreseen human error risk - ruling
A judge investigating Spain's worst train disaster in decades will question safety officials from state rail company Adif after finding basic precautions were not made, papers released on Tuesday showed.
The main cause of the accident, that killed 79 people in the northwestern region of Galicia last month, was the train's excessive speed, judge Luis Alaez wrote in court documents.
But he had also decided to put safety officials at Adif under formal investigation, the papers said.
"There was an omission of elementary precautions by those whose mission it was to guarantee the safety of railway circulation on the line, which could constitute a punishable offence," Alaez wrote.
The train derailed and slammed into a concrete wall on the outskirts of Santiago de Compostela on July 24, after approaching a curve at more than twice the speed limit on that piece of the track.
Driver Francisco Garzon, 52, has been charged with negligent homicide and released without bail pending trial.
In a closed-door hearing before Alaez, Garzon admitted taking the curve too fast, blaming it on a momentary lapse, according to media reports.
Alaez, who is leading a pre-trial investigation of the crash, said those responsible for safety should have foreseen that human errors, caused by fatigue or habit, could pose a risk on what was known to be a difficult curve.
Given the lack of adequate automatic braking systems that could work on that stretch of rail, safety officials should have taken better preventative measures, including brake signs further away from the bend, the judge said.
Adif said it had not yet received an official request from the judge and did not know how many employees might be placed under investigation.
"Adif is collaborating and will collaborate with the judge," its spokesman said.
Adif and train operator Renfe have also been asked to hand over technical reports and documents on security protocols, as well as internal audits and incident reports relating to the track where the accident happened.
Spain's government has started a review of the safety of the whole rail system.