The neighbours had always considered their names odd – Mr and Mrs Anschlag, meaning "attack" – and the fact that she was often seen in the garden of their white-washed, detached, house making phone calls in the depths of winter, caused tongues to wag.

But other than that, Andreas and Heidrun Anschlag hardly triggered the curiosity of any but the most avid curtain twitchers in the community of Marburg, west Germany, where they lived for years.

That was before their spectacular arrest in October 2011 on suspicion of spying for Moscow, when a special forces commando stormed their house.

Heidrun was in the middle of receiving encoded messages on shortwave frequency at the time, prosecutors said. She was reported to have been so shocked she fell off her chair, pulling the connection cable with her.

The trial of the couple opened in Stuttgart, southern Germany, on Tuesday. The pair are accused of passing confidential documents, procured from a Dutch foreign ministry official, to Russian intelligence services.

Over 23 years they are said to have passed thousands of EU, Nato and UN secrets to the former Soviet Union and then Russia, using "dead letter boxes", as well as communicating via satellite and the internet.

According to prosecutors the pair received about €100,000 (£80,000) a year from Moscow. Allegedly they passed on information pertaining to the relationship between the west and countries in eastern Europe and central Asia. The court will hear how the couple built up what prosecutors described as a "bourgeois existence" in Germany at the end of the 1980s and convinced their neighbours that they were Austrian of south American descent – when in fact they were Russian.

Andreas, a car engineer, now 54, worked in various companies, while his wife, now 48, kept house. Even their daughter, a medical student, was said to know nothing of their true existence.

They spoke in court just to confirm their "cover names".

The court does not know their true identity, only that they were known to their spymasters in Moscow as Pit and Tina. Their real forenames are believed to be Sasha and Olga. Pictures of them in the courtroom had to be pixellated for legal reasons.

The couple's most important source of information is believed to have been the Dutch foreign ministry, where a source handed them information once a month. The information is believed to have been placed in special hiding places, known as "dead letter boxes", from where Andreas collected them.

The couple are believed to have transmitted some texts via satellite and to have concealed secret messages in commentaries on YouTube where Heidrun communicated with her controller using the name Alpenkuh1 (alpine cow 1).

Heidrun is believed to have received detailed directives from Moscow twice a week, using a shortwave receiver which was connected to a decoder and computer. While the couple received their messages via radio, they replied via satellite.

Some of their neighbours were believed to have been present in court on Tuesday, keen to learn the full story of the Anschlags and how the cold war had effectively continued right under their noses until 2011.

Mika Beuster, a local journalist, said the story had "all the ingredients of an exciting spy thriller", adding: "The neighbours thought nothing strange about them except for their eastern European accent. There was nothing that would distinguish them from any other family in the town."

He wrote in a commentary for the local paper that the trial would resemble a "tour round a history museum", as the often old-fashioned spying methods the couple are alleged to have used came to light.

The couple are being defended by Horst-Dieter Pötschke, known in Germany as "lawyer to the spies", after he famously defended agents from the east, Stasi officials and members of the KGB. His best-known client was Günter Guillaume, a close aide to the west German chancellor Willy Brandt whose exposure as a Stasi spy in the 1970s led to his downfall.

Pötschke told journalists before the trial that the couple hoped to be swapped for German agents working in Russia. He said his clients would maintain their silence throughout the trial. If convicted, the couple could face up to 10 years in prison.

Prosecutors will be keen to find out what were the couple's information sources. The Dutch messenger who was arrested in March 2012 is due to go on trial in the Netherlands.

The trial continues, scheduled to run until June.