A Russian judge ruled in a closed pretrial hearing Tuesday that US citizen Paul Whelan will remain in Russian custody until his trial.

Whelan has been imprisoned in Russia since December 28, when Russia’s Federal Security Service (FSB) arrested Whelan on suspicion of espionage while he was allegedly visiting Russia for a wedding. Whelan was later charged with espionage on January 3.

Whelan’s lawyer, Vladimir Zherebenkov, told news outlets that before Whelan was arrested, he had accepted a flashdrive containing “state secrets,” on the mistaken belief that the flashdrive contained his personal vacation photos.

In a news conference last Tuesday, Russian Foreign Minister Sergey Lavro stated that the flashdrive proves that Whelan was caught “red-handed” while carrying out illegal activity.

Russian media noted that the possibility that Whelan could be exchanged for accused Russian spy Maria Butina, currently in US custody.