Copper cables used in the signalling system of the Madrid-Seville high-speed line were confiscated at four locations in the Toledo area on Sunday night.
It comes just a week after Spain and neighbouring Portugal suffered an unprecedented and unexplained power blackout.
One passenger who was stuck in a train for ten hours, told daily newspaper El Pais: “The toilets didn’t work and we couldn’t get out of the carriages. We were very cold because they opened the doors and we used our jackets to keep the children warm.”

As state train operator Renfe and the railway infrastructure company Adif rushed to restore services, Spain’s transport minister Óscar Puente urged Spaniards with information to contact the police.
He told radio station Cadena Ser: “Whoever did it knew what they were doing because there were no cameras and the financial gain is absolutely negligible compared with the enormous damage.”
Renfe president Álvaro Fernández Heredia also felt the theft was suspicious, telling Radio Nacional de España: “The theft of signalling cable on which the safety infrastructure depends is sabotage, even if it’s just simple theft because it’s an attack on the infrastructure itself.”
By 9.30am on Monday, the Madrid-Seville line was running again with services expected to return to normal over the course of the day.
Spain’s interior ministry said the Guardia Civil had opened an investigation, adding that it is in regular contact with the Policía Nacional and Adif.
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Spain has to get back to functioning again
Núñez Feijóo
According to official data, there were more than 4,400 thefts involving copper and conductive materials last year.
Meanwhile, the Spanish government, which is led by Prime Minister Pedro Sánchez, claims it needs “several more days” to work out what caused the nationwide blackout on April 28.
The latest incident has prompted the conservative People’s Party to accuse the Socialist Workers' Party administration of incompetence.
Opposition leader Alberto Núñez Feijóo said: “We’ve had two events in the past week that are more commonly seen in countries we wouldn’t want to resemble; countries where the government has forgotten about its citizens.
“Second Monday with images unbefitting of the fourth largest economy in the eurozone … Spain has to get back to functioning again.”