The crash occurred on the eve of annual festivities at the shrine, which subsequently were canceled.
The court spokeswoman said that before taking the driver's testimony, officials carried out checks on calls and messages made from the man's mobile phone.
At least one press photograph showed the man talking on a mobile phone shortly after the crash. Several news media reported Garzon told railway control in a call that he had been going too fast.
Most of the dead were Spaniards but there were also victims from Algeria, Brazil, the Dominican Republic, France, Italy, Mexico and the United States. The train was almost certainly carrying would-be pilgrims although most usually walk to Santiago from all over Spain and abroad.
On Sunday, families of victims performed the painful task of retrieving their loved ones' belongings, collecting luggage that was being held by police.
The Spanish rail agency has said the brakes should have been applied four kilometers (2.5 miles) before the train hit the curve. The witness who rushed to the scene said in an interview broadcast Sunday that minutes after the crash Garzon told him he couldn't brake.
The resident, Evaristo Iglesias, said he and another person accompanied the blood-soaked Garzon to flat ground where other injured people were being laid out, waiting for emergency services to arrive. A photograph shows Iglesias in a pink shirt and cap helping the bloodied driver.
"He told us that he wanted to die," Iglesias told Antena 3 television. "He said he had needed to brake but couldn't," Iglesias said. He added that Garzon said "he had been going fast."
Spain's state-run train company has described Garzon as an experienced driver who knew the route well.