ROME (AP) — Italy’s spy thriller took a decidedly mundane turn Thursday with indications that the Italian Navy captain accused of passing classified documents to Russia was desperate for extra money to pay his mortgage and support his four children.

Walter Biot, an Italian Navy frigate captain most recently assigned to a policy position at the Defense Ministry, was being held at Rome’s Regina Coeli prison. During a preliminary interrogation Thursday, he exercised his right to not answer prosecutors’ questions or make a statement, Italian news reports said.

Biot was arrested on espionage charges Tuesday after he was allegedly caught passing a pen drive of classified documents, including some on NATO operations, to a Russian Embassy official in exchange for 5,000 euros ($5,900). He had been trailed for months by Italian intelligence officials.

A Rome judge on Thursday confirmed his arrest and denied his request for house detention, the ANSA and LaPresse news agencies reported. His lawyer, Roberto De Vita, didn’t immediately respond to calls or an email seeking comment.

The Foreign Ministry immediately ordered the Russian caught with Biot, as well as another Russian Embassy diplomat, expelled in what Foreign Minister Luigi Di Maio said was a “hostile act of extreme gravity.”

Biot’s wife, Claudia Carbonara, insisted that Biot would never betray Italy’s security. But she said he was desperate for money since his 3,000-euro salary at the Defense Ministry simply didn’t cover the needs of a family of six with four dogs and a mortgage.

In an interview with Corriere della Sera newspaper, Carbonara said Biot wouldn’t dream of cutting back on his children’s sports activities but couldn’t make ends meet. Carbonara, a psychotherapist, said if he had told her what he was planning, she would have dissuaded him.

“Even if he did what he did, I’m sure he would have thought it through and wouldn’t prejudice the national interest. He’s not stupid,” she was quoted as saying.

Biot’s adult son, meanwhile, told reporters that his father was only trying to support his family. In an audio recording posted on the website of La Repubblica newspaper, the 24-year-old son said he returned to the family's Pomezia home Tuesday evening to find Carabinieri officers there, and that he only learned his father had been arrested on espionage charges from news reports.

The son, whose name was not given, said neither he nor his adult sister had full-time jobs, working only as a gardener or cleaning pools, leaving Biot to support them all. He voiced concern that if his father receives a dishonorable discharge from the Navy, the family would face even more devastating financial problems.

“If he did something like this, maybe there’s a solution, that he is suffering from mental instability,” he said.