Spanish police have rescued two elderly people who had allegedly been locked up and drugged by a couple who posed as carers while draining more than €1.8m from the bank accounts of a string of victims.

The Guardia Civil was eventually led to what it described as a “house of horrors” after police in Frankfurt asked for help in tracking down a 101-year-old German woman called Maria Babes.

Officers from the Spanish force located Babes in a care home in the town of Chiclana de la Frontera, near the southern city of Cádiz. The elderly woman was seriously ill and her hospital records raised suspicions about the behaviour of the people who had been looking after her before she entered the care home.

An investigation found that a Cuban-German couple, who have not yet been officially named, had befriended Babes in Tenerife and brought her to southern Spain “so that they could control her better”. Police said the couple had used the same technique to take advantage of other vulnerable people.

Once she was well enough to talk, Babes told the Guardia Civil the couple had kept her in a rented house for months, bound by her hands. Unbeknown to their prisoner, they sold her house in Tenerife and took more than €160,000 (£120,000) from her bank account.

A day before officers arrested the couple, the man and woman managed to persuade Babes to leave the care home with them. Within five hours, she was dead.

“The death was strange given that that morning a video was shot showing her in perfectly good health and playing the tambourine during Christmas breakfast in the home,” the Guardia Civil said in a statement.

No postmortem examination was carried out on her body as the couple insisted on an urgent cremation. The undertaker told police he had thought it was odd that the couple had not asked for Babes’ ashes, despite claiming to be very fond of her.

When the Guardia Civil arrived at the rented house, they found two plane tickets to Cuba – and evidence of another rented property close by.

It was there that they found an elderly Dutch woman and an elderly German man in dire hygiene and health condition.

“Both were found in rooms that were bolted shut from outside, and both were being fed through nasal tubes and could not move about,” said the statement.

They are now recovering. The notary who did the paperwork for Babes’ estate identified the Dutch woman as the person who had posed as Babes during the signing over of her assets.

The couple remained in custody. Investigators have come across €1.8m “obtained in similar circumstances” from another four people they had “looked after”.

The Spanish authorities are seeking legal assistance from courts in England, Italy, Germany and Cuba to help determine the scale of the couple’s international finances and holdings.

The couple are accused of crimes including fraud, misappropriation, domestic abuse and money laundering. Four other people have been arrested and a further nine are under investigation.