MOSCOW — Paul Whelan, a former U.S. Marine detained in Moscow on spy charges, was given a flash drive containing a “state secret,” his lawyer said Tuesday, delivering the first official details in a mysterious case that has been wrapped in silence for weeks.

Whelan, 48, who also holds British, Canadian and Irish citizenship, was arrested by Russian security services in late December, during what his family said was a personal trip to the Russian capital. He was later charged with the relatively broad crime of espionage. 

Speaking in a Moscow court, his lawyer Vladimir Zherebenkov told reporters, “How he got [the flash drive], what he was supposed to do with it, and whether Whelan knew that he had secret information is unknown.” 

Zherebenkov said Whelan, a frequent visitor to Russia over the past decade, expected the flash drive to contain photographs and videos of one of his previous trips to the country. He had asked an acquaintance to send him the information because he had been unable to download it electronically.

The Post's Shane Harris discusses Paul Whelan, the man claiming citizenship in four countries who Russia is holding and accuses of being a spy. (Sarah Parnass/The Washington Post)

“He only spoke to regular people in Russia,” Zherebenkov added. 

At the closed-door, pretrial hearing, the Russian court refused to release Whelan on bail, meaning he will remain behind bars through the end of February.

Wearing a blue button-down shirt and glasses, the Michigan resident was held in a metal and glass enclosure, where he looked on as he spoke to his lawyer through an interpreter. 

Whelan spoke in court for 15 minutes and gave a “detailed description of his response to the charges,” Zherebenkov said, adding that Whelan maintains his innocence. Zherebenkov reiterated the claim of Whelan’s family that he was in Moscow for a friend’s wedding and was seized in a hotel room near the Kremlin. 

The case of Whelan, who was court-martialed for stealing thousands of dollars from the U.S. government and received a bad-conduct discharge, has mystified reporters and officials in Russia.  

Former U.S. intelligence officials have said that Whelan’s background, and the fact that he was not in Russia under diplomatic cover, make him an unlikely spy. This led some experts to speculate that he could be traded for a Russian asset in the United States, such as gun rights activist Maria Butina.

Butina, 30, pleaded guilty last month to trying to influence the 2016 presidential campaign. 

Zherebenkov stressed Tuesday that no swaps could take place before a conviction.

The hearing was attended by consular officials from all four countries where Whelan holds citizenship, representing a first for Britain and Canada, which have been denied access to Whelan.